Haematology Flashcards
(425 cards)
1
Q
What cells do pluripotent haemopoietic stem cells give rise to?
A
Lymphoid stem cells
Multipotent myeloid stem cells
2
Q
Where is erythropoietin produced?
A
90% - kidney’s juxtatubular interstitial cell
10% - hepatocyte/interstitial cells
3
Q
What influences bone marrow production of granulocytes and monocytes?
A
Cytokines eg. interleukins and granulocytes
Granulocyte-macrophage colony stimulating factors
4
Q
What are the functions of haemoglobin?
A
Transport of oxygen
Transport of carbon dioxide
Transport of nitric oxide
Acts as a buffer for the blood
5
Q
What the the intravascular life spans for:- Erythrocytes Neutrophils Monocytes Eosinophils Lymphocytes Platelets
A
Erythrocytes- 120 days Neutrophil- 7-10 hours Monocyte- Several days Eosinophil- A little shorter than a neutrophil Lymphocyte- Very variable Platelet- 10 days
6
Q
Define anisocytosis
A
Red cells show more variation in size than is normal
7
Q
Define poikilocytosis
A
Red cells show more variation in shape than is normal
8
Q
What is a microcyte?
A
When the red blood cell’s size is smaller than normal
9
Q
What is microcytic anaemia?
A
Anaemia due to small red blood cells
10
Q
What is macrocytosis?
A
A disorder which is characterised by the presence of macrocytes in the blood
11
Q
Define normochromic
A
Normal cell state
12
Q
What is hypochromia?
A
Red cells have a larger area which is pale than normal (normal cells= 1/3 diameter is pale)
This is due to lower haemoglobin content and concentration and the cell being flatter
13
Q
What is polychromasia?
A
Increased blue tinge to the cytoplasm of a red cell, indicating that the red cell is young
14
Q
What is an elliptocyte?
A
A red blood cell that is elliptical in shape
Occurs in hereditary elliptocytosis and iron deficiencies
15
Q
What is a spherocyte?
A
Cells that are approximately spherical in shape
Have a round, regular outline and lack central pallor
Due to loss of cell membrane without the loss of an equivalent amount of cytoplasm which leads to the cell being forced to round up
16
Q
What is a target cell?
A
Cells with an accumulation of haemoglobin in the centre of the area of pallor
Occur in obstructive jaundice, liver disease, haemoglobinopathies and hyposplenism
17
Q
What is a sickle cell?
A
Result from the polymerisation of haemoglobin S when it is present in high concentrations
Have a sickle shape
18
Q
What is a fragment?
A
Red blood cells that are broken up
e.g. shistocytes
19
Q
Define rouleaux
A
Stacks of red blood cells which resemble a pile of coins
Results from alterations in plasma proteins
20
Q
What is agglutination?
A
Red blood cell agglutinates differ from rouleaux as the clumps are irregular
Result from antibodies on the surface of the cells
21
Q
What is a Howell-Jolly body?
A
A nuclear remnant in a red cell
Usually due to a lack of splenic function
22
Q
What is leucocytosis?
A
Too many white blood cells
23
Q
What is leucopenia?
A
Too few white blood cells
24
Q
Define left shift
A
An increase in non-segmented neutrophils/neutrophil precursors in the blood
25
What is a hypersegmented neutrophil?
An increase in the average number of neutrophil lobes or segments
Usually a result of a lack of vitamin B12 or folic acid
26
Define reticulocytosis
Methylene blue dye binds to reticulum, indicating young cells
27
What is an irregularly contracted cell?
A cell which is irregular in outline but smaller than normal cells and have lost their central pallor
Usually a result of oxidant damage to the cell membrane and to the haemoglobin
28
What is anaemia?
A reduction in the concentration of haemoglobin in the circulating blood below what is normal for a healthy individual of the same age and gender
Associated with a reduction in RBC count and haematocrit or packed cell volume
29
What are the causes of anaemia?
Reduced production of red cells by the bone marrow
Loss of blood from the body
Reduced survival of red cell in the circulation (haemolysis)
Increased pooling of red cells in an enlarged spleen
30
What are the causes of microcytosis?
Defects in haem synthesis
| Defects in globin synthesis
31
What are the causes of macrocytosis?
Megaloblastic anaemia (resulting from a deficiency of vitamin B12 or folic acid)
An increased proportion of reticulocytes prematurely released from the bone marrow
Liver disease
Use of drugs interfering with DNA synthesis
Excess alcohol intake
Recent major blood loss with adequate iron stores
Haemolytic anaemia
32
What are the causes of normocytic anaemia?
Peptic ulcer, oesophageal varices, trama
Failure of production of red cells
Hypersplenism
33
What is haemolytic anaemia?
Anaemia resulting from shortened survival of RBCs in the circulation
Can be caused by defective red cells= intrinsic or
defect outside of red cells= extrinsic
34
How can haemolytic anaemia be classified?
```
Inherited= results from abnormalities in the cell membrane, haemoglobin or intrinsic enzymes
Acquired= results from extrinsic factors such as micro-organisms, chemical or drugs that damage the RBC
Intravascular= haemolysis occurs if there is very acute damage to the red cell
Extravascular= occurs when defective red cell are removed by the spleen
```
35
When should haemolytic anaemia be suspected?
Unexplained anaemia, which is normochromic and either normocytic or macrocytic
Evidence of morphologically abnormal red cells
Evidence of increased red cell breakdown
Evidence of increased red marrow activity
36
How can the diagnosis of haemolytic anaemia be aided?
- The detection of morphologically abnormal red cells (spherocytes, elliptocytes, fragments)
- Evidence of increased red cell breakdown (increased serum bilirubin and lactate dehydrogenase)
Evidence of an increased bone marrow response (polychromasia and an increased reticulocyte count)
37
What are the causes of inherited haemolytic anaemia?
- Abnormal red cell membrane e.g. hereditary spherocytosis
- Abnormal Hb e.g. sickle cell anaemia
- Defect in glycoytic pathway e.g. pyruvate kinase deficiency
- Defect in enzyme of pentose shunt e.g. G6PD deficiency
38
What are the causes of acquired haemolytic anaemia?
- Damage to red cell membrane e.g. AIHA or snake bite
- Damage to whole red cell e.g. MAHA
- Oxidant exposure, damage to red cell membrane and Hb e.g. dapsone or primaquine
39
Is sick cell anaemia inherited or acquired?
Inherited haemolytic anaemia
40
Is pyruvate kinase deficiency inherited or acquired?
Inherited haemolytic anaemia
41
Is glycose-6-phosphate dehydrogenase deficiency inherited or acquired?
Inherited haemolytic anaemia
42
Where is the site of defect in hereditary spherocytosis?
Membrane
43
Where is the site of defect in sickle cell anaemia?
Haemoglobin
44
Where is the site of defect in pyruvate kinase deficiency?
Glycolytic pathway
45
Where is the site of defect in glucose-6-phosphate dehydrogenase deficiency?
Pentose shunt
46
Give examples of acquired haemolytic anaemia
- Autoimmune haemolytic anaemia
- Microangiopathic haemolytic anaemia
- Malaria
- Drugs and chemicals
47
Where is the site of defect and nature of damage in autoimmune haemolytic anaemia?
- Membrane
| - Immune
48
Where is the site of defect and nature of damage in microangiopathic haemolytic anaemia?
- Whole red cells
| - Mechanical
49
Where is the site of defect and nature of damage in haemolytic anaemia caused by drugs and chemicals?
- Whole red cells
| - Oxidant
50
Where is the site of defect and nature of damage in malaria?
- Whole red cell
| - Microbiological
51
What is hereditary spherocytosis?
- Haemolytic anaemia or chronic compensated haemolysis from an INHERITED INTRINSIC defect of the red cell membrane
- After entering the circulation the cells lose membrane in the spleen and therefore become spherocytic
52
Why does extravascular haemolysis occur is hereditary spherocytosis?
Red cells become less flexible and are removed prematurely in the spleen
53
What causes the polychromasia and reticulocytosis in hereditary spherocytosis?
The bone marrow responds to haemolysis by an increased output of red cells
54
What does haemolysis in hereditary spherocytosis cause?
- Increased bilirubin production
- Jaundice
- Gallstones
55
How is hereditary spherocytosis treated?
- Only effective treatment is splenectomy (only done in severe cases as it has risks)
- A good diet is important to prevent secondary folic acid deficiency
- Or, one folic acid tablet can be taken daily
56
What is the purpose of glucose-6-phosphate dehydrogenase?
- Important enzyme in the pentose phosphate shunt
- Essential for the protection of the red cell from oxidant damage
- Oxidants may be generated in the blood stream e.g. during infection or may be exogenous
57
Give examples of extrinsic oxidants
- Foodstuffs (e.g. broad beans)
- Chemicals (e.g. naphthalene
- Drugs (e.g. dapsone, primaquine)
58
Why are patients suffering from glucose-6-phosphate dehydrogenase deficiency usually hemizygous males?
- The gene for G6PD is on the X chromosomes
| - Occasionally seen in homozygous females
59
Why does glucose-6-phosphate dehydrogenase deficiency cause intermittent severe INTRAVASCULAR haemolysis?
A result of infection or exposure to an exogenous oxidant
| - These episodes are associated with the appearance of considerable numbers of irregularly contracted cells
60
How does haemoglobin appear is glucose-6-phosphate deficiency?
- Haemoglobin is denatured and forms round inclusions known as HEINZ BODIES.
- These can be detected by a specific test
- Heinz bodies are removed by the spleen, leaving a defect in the cell
61
What causes autoimmune haemolytic anaemia?
- Results from production of autoantibodies direct at red cell antigens
62
What causes spherocytosis in autoimmune haemolytic anaemia?
The immunoglobulin bound to the red cell membrane is recognised by splenic macrophages, which remove parts of the red cell membrane
63
In autoimmune haemolytic anaemia, what leads to to the removal of cells from the circulation?
- The spherocytes are less flexible than normal red cells
- The combination of cell rigidity and recognition of antibody and complement on the red cell surface by splenic macrophages leads to removal of cells from the circulation by the spleen
64
How is autoimmune haemolytic anaemia diagnosed?
- Finding spherocytes and an increased reticulocyte count
- Detecting immunoglobulin on the red cell surface
- Detecting antibodies to red cell antigens or other autoantibodies in the plasma
65
How is autoimmune haemolytic anaemia treated?
- Use of corticosteroids and other immunosuppressive agents
| - Splenectomy for severe cases
66
What is polycythaemia?
- Literally means 'many cells'
- Refers specifically to many red cells in the circulation
- Hb, RBC and PCV/Hct are all increased compared with normal subjects of the same age and gender
67
How is 'psuedopolycythaemia' or 'apparent polycythaemia' differentiated from true polycythaemia
- Pseudopolycythaemia or apparent polycythaemia= a high Hb, RBC and PCV/Hct resulting from a decrease in plasma volume
True polycythaemia= a high Hb, RBC, PCV/Hct resulting from an increase in the number of circulating red cells
68
What are the causes of polycythaemia?
- Too much blood i.e. blood doping
- Medical negligence
- Too much erythropoietin
- Abnormal function of the bone marrow
69
How is Polycythaemia vera characterised?
- Increased haematocrit in the peripheral blood
- Hypercellular marrow with increased numbers of erythroid megakarocytic, and granulocytic cells
- Variable increase in the number of reticulin fibres
70
How is essential thrombocythemia characterised?
- Increase in the number of platelets in the peripheral blood
- Increased number of megakaryocytes in the marrow, which tend to cluster together and have hyperlobated nuclei
71
How is idiopathic myelofibrosis characterised?
- Presence of immature red and white cells (leukoerythroblastic blood film)
- Teardrop red cells
- Disordered cellular architecture
- Dysplastic megakaryocytes
- New bone formation in the marrow
- Formation of collagen fibres
72
How can too much erythropoietin cause polycythaemia?
- When the action of erythropoietin is appropriately elevated e.g. residents of Tibet
- Erythropoietin appropriately raised as a result of hypoxia
- When erythropoietin is inappropriately administered to haematologically normal subjects (cyclists)
- Renal or other tumour inappropriately secretes erythropoietin
73
Why can polycythaemia from an erythropoietin-secreting renal tumour not surprising?
This is the normal site of erythropoietin production
74
How can abnormal function of the bone marrow result in polycythaemia?
- Inappropriately increased erythropoiesis that is independent, or largely independent of erythropoietin
- This condition is an intrinsic bone marrow disorder= polycythaemia vera
- Classified as a chronic myeloproliferative neoplasm
75
Why can polycythaemia lead to vascular obstruction?
Polycythaemia lead to 'thick blood'- more technically known as hyper-viscosity
76
When would blood be removed in polycythaemia?
- If there is no physiological need for a high haemoglobin
- If hyperviscosity is extreme
- Blood can be removed to thin the blood
77
Why would drugs be used if there is intrinsic bone marrow disease in polycythaemia?
To reduce bone marrow production of red cells
78
What processes are involved in haemostatic plug formation?
1) Vessel constriction
2) Formation of an unstable platelet plug
- Platelet adhesion
- Platelet aggregation
3) Stabilisation of the plug with fibrin
- Blood coagulation
4) Dissolution of clot and vessel repair
- Fibrinolysis
79
What are the functions of the endothelium?
- Maintain barrier between blood and procoagulant subendothelial structures
- Synthesis of PGI2, thrombomodulin, vWF, plasminogen activators
80
Where is vessel constriction in the formation of the haemostatic plug mainly important?
Small blood vessels
81
In the formation of an unstable platelet plug, where do platelets originate?
- The platelet has its origin in the bone marrow?
- Diploid haemopoeitic stem cells undergo nuclear replication without cytoplasmic replication to form multinucleate megakaryocyte precursors
- These then undergo maturation with granulation maturation before migrating to the marrow sinusoids, extending proplatelets through the endothelial wall and fragmenting into platelets in the circulation
82
How many platelets does each megakaryocyte produce?
4000
83
What are the ultrastructural features of platelets?
- Dense granules: ADP very important in haemostatic response
- Alpha granules: important proteins include factor V and vWF
- Surface glycoproteins: mechanism enabling activation of platelet when the tissue is exposed
- Receptor for thrombin: activates the platelets
84
What is the lifespan of a platelet?
10 days
85
What proportion of platelets are sequestered in the spleen?
1/3
86
Which surface membrane glycoproteins are the adhesive and aggregation reactions of platelets mediated through?
GIp, Ib, GIp Ia-IIa, GIp IIb/IIIa
87
What is adhesion?
The initial interaction between platelet and collagen (via GIp1a) involves Von Willebrand Factor
- Platelets can also attach directly to collagen via GIp1a
88
What is activation?
Interaction between platelet and collagen > release of ADP and thromboxane, which activate the platelet > expression of other glycoprotein receptors (eg GIpIIb/IIIa)
89
What is aggregation?
These glycoprotein receptors then act as a molecular glue, leading to the formation of an unstable platelet plug
90
Describe prostaglandin metabolism in palelets
1) Membrane phospholipid is converted to arachidonic acid by PHOSPHOLIPASE
2) Arachidonic acid is converted to endoperoxides by CYCLO OXYGENASE
3) Endoperoxides are converted to thromboxane A2 by THROMBOXANE SYNTHETASE
- Endoperoxides and thromboxane are potent inducers of platelet aggregation when secretion
91
Describe prostaglandin metabolism in endothelial cells
1) Membrane phospholipid is coverted to arachidonic acid by PHOSPHOLIPASE
2) Arachidonic acid is converted is Endoperoxides by CYCLO OXYGENASE
3) Endoperoxides are converted to Prostacyclin by PROSTACYCLIN SYNTHETASE
92
What affect does Prostacyclin have on platelet function?
Is a potent inhibitor of platelet function
93
How does aspirin act as an antiplatelet agent?
Irreversibly inhibits cyclo-ocegenase in the prostaglandin metabolism pathway in platelets
- This prevents the production of endoperoxides and thromboxane which ultimately reduces platelet aggregation
- Anti-platelet agents are extensively used as anti-thrombotics
94
Give examples of antiplatelets used as antithrombotic agents
- COX1 inhibitors e.g. Aspirin
- ADP receptor antagonists eg clopidogrel, prasugrel
- GIpIIb/IIIa antagonists e.g. abciximan, tirofiban, eptifibadatide
95
Give examples of vessel disorders
- Scurvy
- Senile purpura
- Allergic vasculitis (acquired)
- Haemorrhagic telangiectasia
- Ehlers-Danlos syndrome (inherited)
96
What mechanisms can thrombocytopenia (low platelet count) arise from?
1) Failure of platelet production
2) Shortened platelet half life
3) Increased pooling of platelets in an enlarged spleen
97
What can result in failure of platelet production?
- Aplastic anaemia
- Leukaemia
- Vitamin B12/Folate deficiency
98
What tests are used to monitor platelets and their function?
- Platelet count
- Bleeding time
- Platelet aggregation
99
Why is platelet count the most important test when monitoring platelets?
- Progressive reduction of platelets dramatically increases the risk of bleeding
- Used to monitor thrombocytopenia
100
What is the normal range for platelet count?
150-400 x109
101
When is platelet aggregation performed?
To monitor platelet dysfunction and can be used to measure von Willebrand factor activity
102
How is bleeding time performed?
Cuff with 40m pressure is used and a standardised inscision is made on the forearm
103
When is bleeding time performed?
Used to check platelet-vessel wall interaction, when platelet count is normal e.g. renal disease
104
What is normal bleeding time?
Between 3-8 minutes
105
What is seen in auto-immune thrombocytopenia?
Purpura
Multiple bruises
Ecchymoses
106
Where are the sites of synthesis of clotting factors, fibrinolytic factors and inhibitors?
1) The liver- most coagulation proteins
2) Endothelial cells -vWF
3) Megakaryocytes (platelets) - Factor V, vWF
107
Which pathway plays a minimal role in normal haemostasis in vivo?
The intrinsic pathway which is initiated by factor XII activation
108
Describe the coagulation cascade with regards to the extrinsic pathway
- Vessel damage leads to tissue factor being exposed
- This forms an activation with factor VII -> activating the tissue factor/factorVIIa complex
- This activates the extrinsic pathway at the level of factor X -> Xa
(The intrinsic pathway is also activated at factor IX -> IXa)
- The generation of Xa leads to the generation of thrombin (IIa) from prothombin= common pathway
- Thrombin converts fibrinogen to fibrin which is cross-linked by the XIIIa enzyme to form cross-linked fibrin
109
How do platelets accelerate the role of blood coagulation?
Certain clotting factors (factors VII, IX, X and prothrombin bind to membrane phospholipid on the platelets in order to activate their substrate factor
- They accelerate thrombin generation 10,000 fold
110
With regards to phospholipid binding, how can we intervene to slow the amount of thrombin generated?
Phospholipid binding between clotting factors and membrane phospholipids on platelets require Vitamin K dependent post translational modification of certain amino acids which is mediated by Ca2+ ions
111
What is the mode of action of warfarin as an anticoagulant?
- In the presence of vitamin K, an extra carboxyl group is added to a cluster of 9 glutamic acid residues (GIa).
- The carboxyl group binds to calcium which allows binding to the platelet phospholipid membrane which increase the generation of thrombin.
- Warfarin is a vitamin K antagonist, inhibiting post-translational modifications of clotting factors which reduces their activities
112
When is warfarin used?
Long term anticoagulation following venous thrombosis and for treatment of atrial fibrillation
113
What is heparin used for?
Immediate anticoagulation in venous thrombosis and pulmonary embolism
114
How does heparin work?
Accelerates the action of plasma inhibitor antithrombin, thus accelerating the inhibition of thrombin and other clotting factors (XIa, IXa, Xa)
115
What does antithrombin inhibit?
Factor XIa
Factor IXa
Factor IIa (Thrombin)
116
What are the two types of heparin?
1) High molecular weight heparin acts more on factor IIa (thrombin)
2) Low molecular weight heparin acts more on factor Xa
117
What are the different laboratory tests for blood coagulation?
APTT- Activated partial thromboplastin time
PT- Prothrombin time
TCT/TT- Thrombin clotting time
118
How does the APTT test work
Initiates coagulation through factor XII and detects abnormalities in Intrinsic and Common pathways
119
How does the PT test work?
Initiates coagulation through tissue factor and detects abnormalities in Extrinsic and Common pathways
120
How does the TCT test work?
Add thrombin
| Shows abnormality in the fibrinogen to fibrin conversion
121
When would the APTT and PT tests be used together?
Screening for causes of bleeding disorders
122
What does the APTT test monitor?
Heparin therapy in thrombosis
123
What does the PT test monitor?
Warfarin treatment in thrombosis
124
What is fibrinolysis?
Dissolution of the clot and vessel repair in the last stage of normal haemostasis
- Involves plasminogen and tissue plasminogen activator which normally circulate together
- When a fibrin clot forms, the two bind.
- tPA converts plasminogen to plasmin leading to the dissolution of the clot and release of fibrin degradation products
125
What is used in therapeutical thrombolysis for myocardial infarction (clot busters)?
tPa
| Streptokinase (bacterial activator
126
Why does blood not clot completely clot whenever clotting is initiated by vessel injury?
Coagulation inhibitory mechanisms prevent this.
1) Antithrombin
2) The protein C anticoagulant pathway (with protein C and protein S)
127
Name three deficiencies which are risk factors for thrombosis.
1) Antithrombin
2) Protein C
3) Protein S
128
What is the protein C anticoagulant pathway?
Thrombin causes the thombomodulin mediated activation of protein C.
Activated protein C then activates Protein S, which inhibits the phospholipid binding dependent factors VIIIa and Va
129
What are minor bleeding symptoms?
- Easy bruising
- Gum bleeding
- Frequent nosebleeds
- Bleeding after tooth extraction
- Post-operative bleeding
- In women, menorrhagia and post-partum bleeding are also common
130
What are elements of significant bleeding history?
- Epistaxis not stopped by 10 mins compression or requiring medical attention/transfusion
- Cutaneous haemorrhage or bruising without apparent trauma (esp. multiple/large)
- Prolonged (>15 mins) bleeding from trivial wounds, or in oral cavity or recurring spontaneously in 7 days after wound. Spontaneous GI bleeding leading to anaemia
- Menorrhagia requiring treatment or leading to anaemia, not due to structural lesions of the uterus
- Heavy, prolonged or recurrent bleeding after surgery or dental extractions
131
What causes abnormal haemostasis?
1) Lack of a specific factor
- Failure of production: congenital and acquired
- Increased consumption/clearance
2) Defective function of a specific factor
- Genetic defect
- Acquired defect: drugs, synthetic defect, inhibition
132
What is thrombocytopenia a disorder of?
Primary haemostasis
133
What can cause bone marrow failure which results in thrombocytopenia?
Leukaemia
| B12 deficiency
134
What can cause accelerated clearance of platelets- leading to thrombocytopenia?
ITP- Idiopathic thrombocytopenia purpura
DIC- Disseminated intraveascular coagulation
Auto-ITP (autoimmune)
135
What are the mechanisms and causes of thrombocytopenia?
1) Failure of platelet production by megakaryocytes
2) Shortened half life of platelets
3) Increased pooling of platelets in an enlarged spleen (hypersplenism) and shortened half life
136
What can cause impaired function of platelets?
- Hereditary absence of glycoproteins (GIpIIb and GIpIIa receptor absence -> lack of platelet activation) or storage granules (dense granules contain ADP, alpha granules containing vWd factor, factor V)
- Acquired due to drugs
137
Give examples of defects in primary haemostasis where platelet function if impaired
- Glanzmann's thromboasthenia: no GIpIIb/IIIa
- Bernard Soullier syndrome: no GIpIb
- Storage pool disease: affects dense & alpha granules
138
What drugs can leads to impaired function of platelets?
Aspirin
NSAIDS
Clopidogrel
139
What is Von Willebrand disease a disorder of?
Priamary haemostasis
140
What are the functions of Von Willebrand factor in haemostasis?
- Binding to collagen and capturing platelets
| - Stabilising factor VIII (Factor VIII may be low if VWF is very low)
141
What are the characteristics of von Willebrand disease?
- Hereditary disease in quantity of function of vWF
- Type 1 or 3= deficiency
- Type 2= abnormal function
- Autosomal dominant inheritance
- A rare cause is acquired due to antibody
142
What are defects in the vessel wall a disorder of?
Primary haemostasis
143
Give examples of inherited defects in the vessel wall
- More rare
- Hereditary haemorrhagic telangiesctasia, Ehlers Danlos syndrome (really stretchy skin)
- Other connective tissue disorders
144
Give examples of acquired defects of the vessel wall?
- Scurvy
- Steroid therapy
- Ageing (senile purura)
- Vasculitis
145
What are the bleeding symptoms seen in a disorder of primary haemostasis?
- Immediate
- Prolonged bleeding from cuts
- Epistaxes
- Gum bleeding
- Menorrhagia
- Easy bruising
- Prolonged bleeding after trauma or surgery
- Thrombocytopenia > petechiae (small dotted bruising)
- Severe vWD= haemophilia like bleeding
146
What are the test for disorders of primary haemostasis?
- Platelet count
- Bleeding time (PFA100 in lab)
- Assays of von Willebrand factor
- Clinical observation
147
What are defects in coagulation a disorder of?
Secondary haemostasis
148
What is the role of the coagulation cascade?
Generate a burst of thrombin which will convert fibrinogen to fibrin
149
Which coagulation factors are deficient as result of hereditary causes?
- Factor VIII (haemophilia A)
- Factor IX (haemophilia B)
- Factor II (prothrombin)
- Factor XI
- Factor XII
150
What is seen with a deficiency of factor VII and IX?
Haemophilia
- Severe but compatible with life
- Spontaneous joint and muscle bleeding
151
What is seen with a deficiency of prothrombin (factor II)?
It is lethal
152
What is seen with a deficiency in factor XI?
- Bleed after trauma but not spontaneously
153
What is seen with a deficiency in factor XII?
No excess bleeding at all
154
What causes acquired deficiencies of coagulation factors?
1) Liver failure
2) Dilution
3) Anticoagulant drugs
155
Why does liver failure cause decreased production of coagulation factors?
Most coagulation factors are synthesised in the liver
156
Why does dilution result in reduced production of coagulation factors?
- Red cell transfusions no longer contain plasma
| - Major transfusions require plasma as well as rbc and platelets
157
What are the different types of acquired increased consumption causes for a coagulation disorder?
- Disseminated intravascular coagulation
| - Immune (antibodies)
158
What is disseminated intravascular coagulation?
- Generalised activation of coagulation- Tissue factor
- Consumes and depletes coagulation factors
- Platelets consumed
- Activation of fibrinolysis depletes fibrinogen
- Deposition of fibrin in vessel causes organ failure
159
What is disseminated intravascular coagulation associated with?
Sepsis
Major tissue damage
Inflammation
160
What are the characteristics of bleeding in coagulation disorders?
- Superficial cuts do not bleed (platelets)
- Bruising is common, nosebleeds are rare
- Spontaneous bleeding is deep, into muscles and joints
- Bleeding after trauma may be delayed and is prolonged
- Frequently restarts after stopping
161
How is bleeding clinically distinguished between being due to platelet or coagulation defects?
Platelet/vascular:
- Superficial bleeding into skin, mucosal membranes
- Bleeding immediate after injury
Coagulation:
- Bleeding into deep tissues, muscles, joints
- Delayed, but severe bleeding after injury. Bleeding often prolonged.
162
What are the tests for coagulation disorders?
1) Screening tests ('clotting screen')
- Prothrombin time (PT)
- Activated partial thromboplastin time (APTT)
- Full blood count (platelets)
2) Factor assays (for factor VIII etc)
3) Tests for inhibitors
163
How does APTT differ in haemophilia?
It is prolonged significantly
164
Which bleeding disorders are not detected by routine clotting tests?
- Mild factor deficiencies
- von Willebrand disease
- Factor XIII deficiency (cross linking)
- Platelet disorders
- Excessive fibrinolysis
- Vessel wall disorders
- Metabolic disorders (e.g. uraemia)
- Thrombotic disorders)
165
Give an example of a hereditary disorder of fibrinolysis
Antiplasmin deficiency
166
Give examples of acquired disorders of fibrinolysis
- Drugs that enhance tPA
| - Disseminated intravascular coagulation
167
What type of disorder is haemophilia?
Sex linked recessive
| - Only presents in males
168
What type of disorder is von Willebrand disease?
Autosomal
- Type 2 (Type 1) = Autosomal dominant
- Type 3 = Autosomal recessive
169
Why are most bleeding disorders much less common than vWD and haemophilia?
They are autosomal recessive
170
How is abnormal haemostasis due to failure of production/function treated?
1) Replace missing factor/ platelets
- Prophylactic
- Therapeutic
2) Stop drugs
171
How is abnormal haemostasis due to immune destruction treated?
1) Immunosuppression (eg prednisolone)
| 2) Splenectomy for ITP
172
How is abnormal haemostasis due to increased consumption treated?
1) Treat cause
| 2) Replace as necessary
173
What are the principles of factor replacement therapy when treating haemostatic disorders causing bleeding?
1) Plasma
- Contains all coagulation factors
2) Cryoprecipitate
- Rich in fibrinogen, FVII, VWF, Factor XIII
3) Factor concentrates
- Concentrates available for all factors except factor V
4) Recombinant forms of FVIII and FIX are available
174
What haemostatic treatments are available in addition to factor and platelet replacement therapies?
1) DDAVP
2) Tranexamic acid
3) Fibrin glue/spray
175
What is DDAVP?
- Vasopressin derivative
- Results in 2-5x increase in vWF & VIII
- Only useful in mild disorders as it causes the release of endogenous vWF and VIII, not new synthesis
176
What is tranexamic acid?
- Inhibits fibrinolysis
- Widely distributed and crosses the placenta
- Low concentration in breast milk
177
What can a 'normal' range be affected by?
- Age
- Gender
- Ethnic origin
- Physiological status
- Altitude
- Nutritional status
- Cigarette smoking
178
Where is a reference range derived from?
A carefully defined reference population
179
How is a reference range determined?
- Samples are collected from healthy volunteers with defined characteristics
- They are analysed using the instrument and techniques that will be used fro patient samples
- The data are analysed by an appropriate technique
180
What is an appropriate statistical technique?
- Data with normal (Gaussian) distribution can be analysed by determining the mean and standard deviation and taking mean ± 2SD as the 95% range
- Data with a different distribution must be analysed by an alternate method
181
What type of distribution does Hb show?
Gaussian
182
What type of distribution do WBCs show?
non-Gaussian
183
What is PCV?
Packed cell volume
| - Proportion of a column of centrifuged blood occupied by red cells
184
What points should be remembered when interpreting laboratory data?
- A value within the normal range may be abnormal for that individual
- A value outside the normal range may be normal for that individual
- Reference ranges for healthy and sick individuals usually overlap
- Some haematological variables are dependent on the precise instrument or methodology used
185
What is mean cell haemoglobin (MCH)?
The amount of haemoglobin in a given volume of blood divided by the number of red cells in the same volume i.e. the Hb divided by the RBC
186
What is Mean cell haemoglobin concentration (MCHC)?
The amount of haemoglobin in a given volume divided by the proportion of the sample represented by the red cells i.e. the Hb divided by the PCV or haematocrit
187
What is the difference between MCH and the MCHC?
- The MCH is the ABSOLUTE AMOUNT of haemoglobin in an individual red cell
- In microcytic and macrocytic anaemias, the MCH tends to parallel the MCV
- The MCHC is the concentration of haemoglobin in a red cell
- MCH measures the average amount of haemoglobin in an individual red cell
- MCHC is related to the shape of the cell
188
What protein contain iron?
```
Haemoglobin
Myoglobin
catalase
Cytochrome P450
Cytochrome a,b,c
Cyclo-oxygenase
Succinate dehydrogenase
Ribonucleotide reductase
```
189
Why is iron an essential element in proteins?
Its ability to gain and lose electrons easily
| Its ability to bind oxygen
190
What is the structure of haemoglobin?
Each globin chain associates with a single haem group, which is associated with an iron molecule
191
What does haem consist of?
Ring of carbon, hydrogen and nitrogen atoms and in its centre is an iron atom in the ferrous state
192
How long do red cell live for?
120 days
193
How much iron is needed to remake huge number of red cells on a daily basis?
20 mg iron/day
| - However iron is recycled
194
How is iron lost?
1) Desquamated cells of skin and gut
| 2) Bleeding- menstruation
195
How much iron is needed for men and women?
Men- 1mg/day
| Women- 2mg/day
196
How much iron does the human diet provide?
12-15mg/day
197
What natural foods does iron occur in?
- Meat and fish (haem iron)
- Vegetables
- Whole grain cereal
- Chocolate
198
What form of iron can be absorbed?
Ferrous- Fe2+
199
What factors affect iron absorption?
Diet: increase in haem iron and ferrous iron
Intestine: acid (duodenum), ligand (meat
Systemic: Iron deficiency, anaemia/hypoxia, pregnancy
200
What is the iron exporter in mammals?
Ferroportin
201
What is ferroportin controlled by?
Peptide hormone- hepcidin
| - 25 amino acid hormone which is highly conserved in all vertebrates
202
What happens when hepcidin binds to ferroportin
Induced its degradation.
| When this happens iron is stuck in the enterocytes. When it is shed the iron is effectively lost from the body.
203
What happens when iron is absorbed into duodenal cells?
Stored in cells as ferritin
| Or transported bound to transferrin
204
What is transferrin?
Glycoprotein made in the liver with two binding sites for iron.
- Holds onto iron in the circulation, interacting with a transferrin receptor on the surface of erythroblasts
- Transferrin-receptor complex is then internalised and the iron is removed from the transferrin (which is then recycled)
205
What are the roles of iron?
- Positive regulator of erythropoietin
- Positive regulator of expression for the gene that codes for ferritin
- Negative regulator for the expression of the gene that codes for transferrin receptor
206
What is erythropoietin?
A hormone produced in response to anaemia.
| Anaemia -> tissue hypoxia -> Increase in erythropoietin -> red cell precursors
207
What is anaemia of chronic disease?
Anaemia in patients who are unwell
- No bleeding
- No marrow infiltration
- Not iron/B12 or folate deficient
208
What are the laboratory signs of anaemia of chronic disease?
1) C-reactive protein
2) Erythrocyte Sedimentation Rate
3) Acute phase response, increases in:
- ferritin
- FVII
- fibrinogen
- immunoglobulins
209
What conditions are associated with anaemia of chronic disease?
1) Chronic infections e.g. TB/HIV
2) Chronic inflammation e.g. RhA/SLE
3) Malignancy
4) Miscellaneous e.g. cardiac failure
210
What is the pathogenesis of anaemia of chronic disease related to?
Cytokine production
Cytokines released in response to chronic infection prevent the usual flow of iron from the duodenum to red cells.
This is a block in iron utilisation
211
How does cytokine production in anaemia of chronic disease prevent flow?
Blocks iron utilisation. This prevents flow by :
- Stop erythropoietin increasing: less red cells are made
- Stop iron flowing out of cells: less availability of iron
- Increase production of ferritin: increased storage
- Increase death of red cells: fewer red cells
212
What do cytokines include?
TNF alpha
| Interleukins
213
What are the causes of iron deficiency?
1) Bleeding e.g. menstrual/GI
2) Increased use e.g. growth/pregnancy
3) Dietary deficiency e.g. vegetarian
4) Malabsorption e.g. coeliac
214
What are the full GI investigations for iron deficiency?
- Upper GI endoscopy- oesophagus, stomach, duodenum
- Take duodenal biopsy
- Colonoscopy
215
What type of patients will have a full GI investigation for iron deficiency?
- Male
- Women over 40
- Post menopausal women
- Women with scanty menstrual loss
216
What are the laboratory parameters for iron deficiency?
1) MCV
2) Serum iron
3) Ferritin
4) Transferrin (total iron binding capacity, TIBC)
5) Transferrin saturation
217
What are the causes of a low MCV?
1) Iron deficiency
2) Thalassaemia trait
3) Anaemia of chronic disease
218
How is thalassaemia trait confirmed?
- Haemoglobin electrophoresis
| - Confirms an additional type of haemoglobin is present
219
What are the characteristics of serum iron in iron deficiency, anaemia of chronic disease and thalassaemia?
Iron deficiency= low
ACD= low
Thalassaemia= high
220
What are the characteristics of ferritin in iron deficiency and anaemia of chronic disease
Iron deficiency=low
| ACD= high
221
Why is ferritin not always a defining confirmation for iron deficiency?
A bleeding ulcer in rheumatoid arthritis will show a normal ferritin despite iron deficiency.
222
What lab clues indicate the ferritin values should be ignore
1) Raising C-reactive protein
| 2) Raised erythrocyte sedimentation rate
223
How is transferrin used to distinguish between iron deficiency and chronic disease?
Iron deficiency= transferrin goes up
| Chronic disease = transferring is normal or low
224
Describe transferrin saturation in iron deficiency and chronic disease
Iron deficiency= Low saturation
| Chronic disease= normal
225
What further investigations take place if someone if iron deficient?
1) Endoscopy and colonoscopy
2) Duodenal biopsy
3) Anti-coeliac antibodies
4) Anti-helicobacter antibodies
226
What are the characteristics of a classic iron deficiency?
```
Hb= Low
MCV= Low
Serum iron= Low
Ferritin= Low
Transferrin= High
Transferrin saturation= Low
```
227
What are the characteristics of a classic anaemia of chronic disease?
```
Hb= Low
MCV= Low or Normal
Serum iron= Low
Ferritin= High or Normal
Transferrin= Normal/low
Transferrin saturation= Normal
```
228
What are the characteristics of a classic thalassaemia trait?
```
Hb= Low
MCV= Low
Serum iron= Normal
Ferritin= Normal
Tranferrin= Normal
Transferrin saturation= Normal
```
229
What are the characteristics of a bleeding ulcer in rheumatoid arthritis?
```
Hb= Low
MCV= Low
Serum iron= Low
Ferritin= Normal
Transferrin saturation= Low
```
230
What is haemopoiesis?
Production of blood cells in marrow?
231
What is normal haemopoiesis?
Polyclonal/healthy/reaction
- Normal marrow
- Reactive marrow
232
Malignant haemopoiesis?
Abnormal/clonal
- Leukaemia (lymphoid/myeloid)
Myelodyplasia, myeloproliferative
233
How does a myeloblast differentiate into a neutrophil?
1) Myelobalast
2) Promyelocyte
3) Myelocyte
4) Metamyelocyte
5) Neutrophil
234
What are the different types of white blood cells?
```
Immunocytes:
- T lymphocytes
- B lymphocytes
- NK cells
Phagocytes:
- Granulocytes: neutrophils, eosinophils, basophils
- Monocytes
```
235
What results in increased white cell production?
Reactive: infection, inflammation
Malignant: Leukaemia, myeloproliverative
236
What results in a decrease white cell production?
- Impaired bone marrow function
- B12 or folate deficiency
- BM failure: aplastic anaemia, post chemotherapy, metastatic cancer, haematological cancer
237
What reduces cell survival?
An increased immune breakdown
238
What increases cell survival?
Failure of apoptosis
| eg acquired cancer causing mutations in some lymphomas
239
What are the two types of causes of eosinophilia?
Reactive- Still normal haemopoiesis
| Primary- Malignant, the result of abnormal haemopoiesis
240
What is normal haemopoiesis stimulated by?
- Inflammation
- Infection
- Increased cytokine production (distant tumour, haemopoietic or no haemopoietic)
241
What causes abnormal haemopoiesis?
- Cancers of haemopoietic cells
- Leukaemia (myeloid or lymphoid, chronic or acute)
- Myeloproliferative disorders
242
How is a raised white cell count investigated?
- History and examination
- Haemoglobin and platelet count
- Automated differential
- Examine blood film
243
What is a normal full blood count?
```
Hb 120-160g/l
Platelets 150-400 x 109/l
WCC 4-11 x 109/l
Neutrophils 2.5-7.5 x 109/l
Lymphocytes 1.5-3.5 x 109/l
Monocytes 0.2-0.8 x 109/l
Eosinophils 0.04-0.44 x 109/l
Basophils 0.01-0.1 x 109/l
```
244
What are common causes of abnormal white cell counts?
- Phagocytes (neutrophils, eosinophils, monocytes)
| - Immune cells (lymphocytes)
245
What is the life span of a neutrophil?
2-3 days in tissues
| Hours in peripheral blood
246
How much of neutrophils are not counted in the full blood count?
50%
247
What is the nature of the development of neutrophilia?
- Minute for demargination to occur
- Hours for early release from bone marrow
- Days for increased production (x3 in infection)
248
What is neutrophilia?
An absolute neutrophil count >> 7.5 x109/l in adults
249
What is eosinophilia?
An eosinophil count > 0.4 x109/l
250
What are the causes of neutrophilia?
- Infection
- Tissue inflammation (e.g. colitis, pancreatitis)
- Physical stress, adrenaline, corticosteroids
- Underlying neoplasia
- Malignant neutrophilia
- Myeloproliferative disorders
- CML
251
What infections do not produce a neutrophilia?
Brucella
| Typhoid
252
What are the causes of eosinophilia?
1) Reactive
- Parasitic infestation
- Allergic diseases e.g. asthma, rheumatoid, polyarteritis, pulmonary eosinophilia
- Neoplasms esp Hodgkin's, T-cell NHL
- Hypereosinophilic syndrom
2) Malignant Chronic Eosinophilic Leukaemia (PDGFR fusion gene)
253
What can monocytosis occur in?
- TB, brucella, Typhoid
- Viral: CMV, varicella zoster
- Sarcoidosis
- Chronic myelomonocytic leukaemia (MDS)
254
Which phagocytes raise as a result of infection?
```
Neutrophils= Bacterial
Eosinophils= Parasitic
Basophils= Pox viruses
Monocytes= Chronic (TB, Brucella)
```
255
Which phagocytes raise as a result of inflammation?
```
Neutrophils= Autoimmune, tissue necrosis
Eosinophils= Allergic (asthma, atopy, drug, drug reactions
```
256
What phagocytes raise as a result of neoplasia (cells not part of malignant population)?
```
Neutrophils= all types
Eosinophils= Hodgkin's NHL
```
257
What is the cause of mature lymphocytosis?
- Reactive to infection
| - Primary disorder (malignant clonal proliferation of lymphocytes)
258
What is the cause of immature lymphocytosis?
- Primary disorder (leukaemia/lymphoma)
259
Why may lymphocytosis of mature cells occur?
```
Secondary= polyclonal response to infection, chronic inflammation or underlying malignancy
Primary= Monoclonal lymphoid proliferation e.g. CLL
```
260
What are the causes of reactive lymphocytosis?
1) Infection
- EBV, CMV, Toxoplasma
- Infectious hepatitis, rubella, herpes infections
- Autoimmune disorders
- Neoplasia
- Sarcoidosis
261
How does Glandular fever occur?
- EBV infection of B lymphocytes via CD21 receptor
- Infected B-cell proliferates and expresses EBV associated antigens
- Cytotoxic T lymphocyte response
- Acute infection resolved resulting in lifelong sub clinical infection
262
How do laboratory investigations distinguish between primary and secondary/reactive lymphocytosis?
- Morphology
- Immunophenotype
- Gene re-arrangement
263
How do laboratory tests distinguish between monoclonal (primary) and polyclonal (secondary) lymphocytes?
Monoclonal shows only one light chain on the cell surface- kappa or lambda
Polyclonal show a mixed population of kappa or lambda expressing cells
264
How is the gene rearrangement of lymphocytes identified?
- Tell cell receptor genes undergo recombination in antigen stimulated T cells.
With primary monoclonal proliferation, the daughter cells carry identical configuration of TCR genes
- This can be detected by Southern blot analysis
265
Why is the ABO blood system important?
- People have naturally occurring antibodies that are IgM reactive and capable of activating complement.
- Therefore they can cause potentially fatal haemolysis if incompatible blood is transfused
266
What causes a blood group?
- Red blood cells have a common glycoprotein and fucose stem (H stem) on their cell membrane.
- The blood groups are determined by the presence of antigens forms by added one or other sugar residue on the H stem
267
What antigens are in blood group O?
No additional antigens on H stem
268
What antigens are on Blood group A?
A antigen on H stem
| - The A gene codes for an enzyme which adds N-acetylglactosamine to common glycoprotein and fucose stem?
269
What antigens are on Blood group B?
B antigen on H stem
| - B gene codes for enzyme which adds galactose
270
How do the A and B genes interact with each other?
They are co-dominant
271
What type of gene is the O gene?
Recessive
272
What antibodies are present in people?
Antibodies to whatever antigens are NOT present on their H stem
- In group O there are anti-A and anti-B antibodies
273
What antibodies are present in type AB people?
No antibodies
274
How do IgM antibodies interact in laboratory tests?
They interact with their corresponding antigen to cause agglutination.
- A group B patient will agglutinate with group A cells
275
When a patients serum is mixed with donor red cells, what reaction shows it is not a match?
If it agglutinates
276
What is the Rh system?
Looks at the antigens C,D and E
| The most important is D
277
What antigen is present in RhD positive and negative blood group?
RhD postive= D antigen present
| RhD negative= D antigen not present
278
What genes code for RhD group?
D- codes for D antigen on red cell membrane
| d- codes for no antigen and is receddive
279
What percentage of people of RhD positive?
85%
280
How can RhD negative people make anti-D antibodies?
After they are exposed to the RhD antigen.
| Either by transfusion of the RhD positive blood or in women, if they are pregnant with an RhD positive feotus
281
What are Anti-D antibodies?
IgG antibodies
282
In people who make Anti-D antibodies, what care must be taken with future transfusions?
Patient must have RhD negative blood
- Otherwise the anti-D antibodies will react wth RhD positive blood.
- This would cause a delayed haemolytic transfusion reaction- anaemia, high bilirubin, jaundice etc
283
What is haemolytic disease of the Newborn?
If a RhD negative mother has Anti-D antibodies and her next pregnancy the foetus is RhD positive.
- IgG antibodies will cross the placenta and cause haemolysis of foetal blood cells which can lead to death
284
Why can O blood group be used on anyone?
Has no anti-A, anti-B or anti-D antibodies
285
How do you know if a patient will need antigen negative blood?
- Before each transfusion episodes, test a patient's blood sample for red cell antibodies
- Therefore, before transfusing the patient, as well as testing their ABO and RhD group, must do an 'antibody screen' of their plasma
286
What three products are derived from a donation of whole blood?
Red cells
Platelets
Plasma
287
What 3 products are derived from a donation of plasma?
FFP (fresh frozen plasma)
Cryoprecipitate
Plasma for fractionation
288
What is derived from plasma for fractionation?
Albumin
289
What is the shelf life of a blood donation?
5 weeks
| - Stored at 4 degrees
290
What is the shelf life of FFP?
2 years- stored at -30 degrees
291
What are the indications of FFP?
- Should only be given to patients who are bleeding actively and have abnormal clotting tests or are receiving anticoagulant therapy (warfarin) and need urgent surgery
292
How is cryoprecipitate separated from other plasma constituents?
Freezing FFP and then allowing it to thaw at 4-8 degrees overnight.
Approx 3% of FFP forms a residue and fails to redissolve which is the cryoprecipitate
293
What does cryoprecipitate contain?
Factor VIII and fibrinogen
294
What are the indications for the use of cryoprecipitate?
- Massive bleeding
- Fibrinogen deficiency
- Treatment of DIC, together with other blood components
295
What forms are platelet donations available in?
- One pool from 4 donors to constitute a single adult dose
| - A single donor cell by cell separator machine. Equivalent to 4 single donations of platelets
296
What are the indications for the use of platelets?
- Most haematology patients with bone marrow failure (if platelets
297
What are the fractionated products of plasma?
- Albumin
- Factor VIII concentrate
- Factor IX concentrate
- Normal human immunoglobulin
- Specific immunoglobulin
298
What are the clinical uses of Factor VIII and IX?
- For haemophilia A and B (males)
- Factor VIII for vWD
- Heat treated-viral inactivation
- Recombinant factor VIII or IX alternatives increasingly used but are expensive
299
What are the clinical uses of immunoglobulins?
IM: Specific- tetanus, anti-D, rabies
IM: normal globulin- broad mix in population
IVIg- pre-op in patients with ITP or AIHA
300
What are the clinical uses of albumin?
4.5%
- Useful in burns, plasma exchanges
- Probably overused
20% (salt poor)
- For certain severe liver and kidney conditions only
301
How are donors questions before providing a sample?
1) Aim to keep blood safe for patient (eg tansmitting infections, drugs, disease
2) Aim to prevent harm to donors, by questioning to exclude risky one (people who have heart problems)
302
What infections is all blood tested for?
- Hepatitis B (HBsAg, PCR)
- Hepatitis C (anti-HSV,PCR)
- HIV (anti-HCV, PCR)
- HTLV (anti-HTLV)
- Syphilis (TPHA)
- Some also tests for CMV virus
303
Why can testing for infections in donors not be solely relied upon?
The window period infections where tests will not show up as positive
304
How is the risk of vCJD through transfusion in the UK reduced?
- Plasma from UK donors no longer used for fractionation, but rather from USA
- Al blood products are leucodepleted to remove white blood cells as they are vital for the uptake of prions to the brain
305
What is Vitamin B12
- Cobalamin
| - Bacterial product ingested and stored by animals
306
What are good sources of Vitamin B12?
Meat, salmon, cod, milk, cheese, eggs
307
What can cause deficiency of Vitamin B12?
Dietary in vegans
| Malabsorption
308
How much Vitamin B12 is needed by adults
1.5-3 μg a day
309
What is vitamin B12 required for?
DNA synthesis
| Integrity of the nervous system
310
What is folic acid?
- Folate polyglutamates
| - Themolabile water soluble vitamin found in leafy green vegetables
311
What causes folate deficiency?
Dietary
Impaired Absorption
Increased requirement
312
What is folic acid required for?
DNA synthesis
| Homocysteine metabolism
313
How is Vitamin B12 absorbed?
- After ingestion, vitamin B12 is bound in the mouth to haptocorrin, from which is becomes disassociated in the stomach due to gastric enzymes and acid
- The haptocorrin is replaced by intrinsic factoror which is secreted by the parietal cells of the stomach.
- The vitamin-B12-intrinsic-factor complex attaches to the receptor cubulin. Cubulin is present on the surface of epithelial cells of the terminal ileum and facilitates the absorption of the vitamin B12-intrinsic-factor complex
- Intrinsic factor is degraded within the ileal cells and bitamin B12 is absorbed into the bloodstream
- Here is is bound to transcoalamin II which transports it to the various organs for DNA synthesis
314
How is folate absorbed?
- Folic acid (as folate polyglutamates) is hydrolysed to monoglutamates at acid pH
- Folates are absorbed as pteroglutamates which can be methylates in the luminal cells to tetrahydrofolates
315
How is vitamin B12 involved in DNA synthesis?
B12 acts as a cofactor for methionine synthetase in the production of methionine from homocyteine
316
What are the clinical features of vitamin B12 and folate deficiency?
1) Anaemia (macrocytic, megabaloblastic)
- Weak, tired, short of breath
2) Jaundice
- Ineffective erythropoiesis (RBC precursors break down)
3) Glossitis and angular cheilosis
4) Weight loss, change of bowel habit
6) Sterility
317
What shape are the macrocytes in Macrocytic anaemia due to vitamin B12/folate deficiency?
Oval
| - Nitrous oxide destroys methylcobalamin which results in the acute megaloblastic change
318
What shape are the macrocytes in macrocytic anaemia due to liver disease or alcohol?
Round
319
What haematological disorders can be associated with macrocytic anaemia?
- Myelodysplasia
- Aplastic anaemia
- Reticulocytosis
320
What is megaloblastic?
Describes a morphological change in the red cell precursors within the bone marrow
321
What is an erythroblast?
Red cell precursor
322
What is a normoblast?
An early/intermediate/late red cell
323
What is a reticulocyte?
Young red cell with no nucleus
324
What is megaloblastic anaemia?
Asynchronous maturation of the nucleus and cytoplasm in the erythroid (red cell) series
- Nuclear chromatin is immature for the degree of haemoglobinisation of the cytoplasm
325
What are the causes of a raised mean cell volume?
- Vitamin B12 or folate deficiency
- Liver disease
- Hypothyroidism
- Excessive alcohol consumption
- Drugs eg azathioprine (immunosuppressive)
Haematological disorders
326
What is the mechanism of megaloblastic anaemia?
- Delay in DNA synthesis
327
What happens to the red cells and red cell precursors in megaloblastic anaemia?
- Increase size of red cell precursors at all stages of maturation
- A delay in nuclear maturation so the nuclear material (chromatin) is not clumped an appears 'open'
- An increase in the activity of the bone marrow because haemopoiesis is inefective (dysplastic)
- Phagocytosis of dysplastic red cell precursors
328
What happens to white cells and white cell precursors in megaloblastic anaemia?
- Giant metamyelocyes and hypersegmented neutrophils
329
Why is there a fall in MCV as the megaloblastic change progresses?
Red cell fragmentation/pokilocytosis
330
What investigations would you do for macrocytosis?
1) Thyroid function- thyroid disease can be a cause of megaloblastic red cells
2) Liver function
3) Blood film
4) Folate and B12 levels
331
What type of neutrophils are seen in megaloblastic anaemia?
Hypersegmented neutrophils
332
Why may someone be deficient in folate?
- Not enough folate in the diet
- Not absorbing folate properyl
- Increase demand for folate
333
What groups are at risk of dietary folate deficiency?
- Elderly
- Sick
- Eating disorders
- Alcoholics
334
Why does decreased folate availability affect DNA synthesis?
Decreased availability at cellular levels leads to the inability to methylate nucleotides and affects DNA synthesis
335
What are the physiological causes for an increased demand in folate?
(Rapid increase in growth)
- Pregnancy
- Adolescence
- Premature babies
336
What are the pathological causes for an increased demand in folate?
(Rapid cell turnover)
- Malignancy
- Erythoderma- whole body skin rask
- Haemolytic anaemia (sick cell disease, hereditary sherocytosis, autoimmune haemolysis)
337
What are the consequences of malabsorption combined with iron deficiency in coeliac disease?
- Sensitivity to gliadin in wheat causes loss of villi in duodenum
- Anti-gliadin (transglutaminase) antibodies or duodenal bipsy
338
What effect does surgery or inflammatory bowel disease have on folate absorption?
Inteferes with normal absorption in jejunum or upper small bowel
339
What drugs leads to folate malabsorption/
Colestyramine, silfasalazine, methotrexate.
- Trimethoprim may exacerbate pre-existing folate deficiency but does not cause megaloblastic anaemia
- Anticonvulsants, nitrofurantoin and possibly alcohol.
340
What tests are used to establish deficiency?
1) FBC and film
2) Blood folate level
- Serum folate
- Useful as screening test
- Diurnal variation and is affected by recent changes in diet
- Folate supplements rapidly correct serum folate
3) Low red cell folate is diagnostic
- Useful as a confirmatory test
- Low RCF and high serum folate is typical of B12 deficiency
341
What are the consequences of folate deficiency?
1) Megaloblastic anaemia
- Look for low white cells and plaetelet too
2) Neural tube defects
- Folate intake before and during pregnancy
3) Increased risk of venous thromboembolism
342
When and where to neural tube defects occur?
- During faulty embryogenesis
Spine- Spina bifida
Brain- Anencephaly
Therefore all pregnant women take folic acid prior to conception and for the first 12 weeks
343
What effect does folate deficiency have on homocyteine?
It cannot be converted into methionine and therefore builds up intracellularly in the plasma
344
What are very high homocytsteine levels independently associated with?
- Atherosclerosis
| - Premature vascular disease
345
What are mildly elevated levels of homocysteine associated with?
- Cardiovascular disease DEFINITELY
- Arterial thrombosis PROBABLY
- Venous thrombosis POSSIBLY
346
Why may B12 deficiency occur?
- Not enough B12 in the diet
| - Not absorbing B12 properly
347
What is dietary B12 deficiency common in?
- Vegan vegetarians who do not take supplementary vitamins
- Veganism: no food of animal origin, exclude dairy/eggs
- May be linked cultural norms in some religious groups, Hinduism, Buddhism
348
What are the autoimmune causes for B12 malabsorption?
Pernicious anaemia- lacks intrinsic factor
349
What surgeries can affect normal B12 absorption?
- Partial/total gastrectomy
- Gastric bypass surgery
- Resection of ileum
350
What inflammatory disease can affect normal B12 absorption?
Crohn's disease
Chronic pancreatitis
Bacterial overgrowth (blind loop)
Parasitic infection
351
What are the consequences of B12 deficiency?
1) Macrocytic and megaloblastic anaemia
- Reversible with treatment
2) Neurological problems due to demyelination
- Not always reversible with treatment
- Subacute combined degeneration affecting the posterior/dorsal and lateral/pyramidal tracts of the cervical and thoracic spinal cord
- Neuropathy of cranial and peripheral nerves
- Cognitive impairment due to loss of white matter in central nervous system
- Optic atrophy
352
What happens in subacute combined degeneration of the spinal cord?
Results in loss of joint position sense and vibration sense
| - Patient may have a wide-based gait and sometimes pain
353
What are the symptoms of B12 deficiency?
- Weak, tired, lethargic
- Symmetrical paraestesiae/numness
- Muscle weakness
- Difficulty walking and loss of balance
- Visual impairment
- Memory impairment
- Psychiatric disturbance
354
What are the signs of B12 deficiency?
1) Anaemia and jaundice give a 'lemon-yellow' tinge
2) Neurology (legs>arms)
- Loss of vibration and joint position sense but also cutaneous sensation loss
- Absent reflexes and up going plantar responses in legs
355
What tests establish B12 deficiency?
Serum B12 (cobalamin) level
1) Poor positive predictive value
- Healthy persons with low level
- Low levels with no deficiency
2) Falsely high levels in B12 deficient patients
- Due to high levels of autoantibodies interfering with commercial assays
356
What is pernicious anaemia?
Autoimmune atrophic gastritis with loss of intrinsic factor
| - Results in macrocytic/megaloblastic anaemia +/- neurological damage
357
What are the auto-antibodies in pernicious anaemia?
- Intrinsic factor antibodies
| - Parietal cell antibodies
358
How is folate deficiency treated?
- Oral folate or oral cynacobalamin for dietary deficiency or increased requirements
- Parenteral (IM/SC) hydroxycobalamin for malabsorption due to pericious anaemia or bowel disease
359
What is Beta-s?
- Point mutation at codon 6 of the gene for beta globin
- Glutamic acid is replaced by valine
- Whereas glutamic acid is polar and soluble, valine is non polar and insoluble
- Sickle cell haemoglobin
360
How does sickle cell haemoglobin differ from HbA?
Hb exists in two conformations: deoxyHb and oxyHb
This markedly reduces the solubility of deoxyhaemoglobin
- Deoxyhaemoglobin S is insoluble as HbS polymerises to form fibres called tactoids
361
What are the stages in the sickling of red cells?
1) Distortion
- Polymerisation initially reversibly with formation of oxyHbS
- Subsequently irreversible
2) Dehydration
3) Increased adherence to vascular endothelium
362
What is sickle cell disease?
The general term that covers condition that lead to formation of sickled red cells, such as Sickle cell anaemia.
And the compound heterozygous states e.g. SC and S-b thalasseamia
363
What is sickle cell anaemia?
The condition in which there are two βS genes and no normal B genes so the individual cannot produce any normal B chains.
Therefore they cannot produce any HbA
364
What is the pathogenesis of sickle cell disorders?
1) Shortened red cell lifespan-haemolysis
- Anaemia
- Gallstones
- Aplastic crisis
2) Blockage to microvascular circulation
- Tissue damage and necrosis (infarction)
- Pain
- Dysfunction
365
How do sickled cells lead to infarction?
They are sticky and clog up blood vessels and lead to tissue death.
It is associated with severe pain and loss of function
366
What are the consequences of tissue infarction?
1) Spleen
- Hyposplenism (infection)
2) Bones/Joints
a) Dactylitis
b) Avascular necrosis
c) Osteomyelitis
3) Skin
- Ulceration
367
What are the effects of sickling in eyes?
Proliferative retinopathy
368
Why does pulmonary hypertension correlate with the severity of haemolysis?
The free plasma haemoglobin resulting from intravascular haemolysis scavenges NO and cases vasoconstriction
369
When do clinical problems with sickle cell disorders start?
4-6 months as the HbF disappears and the HbS predominates
370
What are the most classical problems in children with sickle cell disorders?
Painful dactylitis
371
How can sequestration and aplastic crises be distinguished between?
The presence/absence of reticulocytes but both require urgent transfusion
372
What are painful crises due to sickle cell disease triggered by?
- Infection
- Exertion
- Dehydration
- Hypoxia
- Psychological stress
373
What is the median survival for sickle cell disease
```
Females= 48 years
Males= 42 years
```
374
What general measures are taken to manage sickle cell disease?
- Folic acid
- Penicillin
- Vaccination
- Monitor spleen size
- Blood transfusion for acute anaemic events, chest syndrome and stroke
- Pregnancy care
375
How is early mortality due to sickle cell disease prevented against?
- Prophylaxis against pneumococcal infection
| - Monitoring for acute splenic sequestration
376
How are painful crises due to sickle cell disease managed?
- Pain relief (opioids)
- Hydration
- Keep warm
- Oxygen if hypoxic
- Exclude infection (blood and urine cultures, CXR)
- Exchange tran
377
When should stem cell transplantation be considered in sickle cell disease?
In Children
378
What are the laboratory features of sickle cell disease?
1) Hb low (typically 6-8g/dl)
2) Reticulocytes high (except in aplastic crisis)
3) Film
- Sickled cells
- Boat cells
- Target cells
- Howell Jolly bodies
379
How is sickle cell disease diagnosed in a solubility test?
- In presence of a reducing agent oxyHb is converted to deoxy Hb
- Solubility decreases
- Solution becomes turbid
- Does not differentiate between sickle cell trait and sickle cell anaemia
380
How is sickle cell disease definitively diagnosed?
Electrophoresis or high performance liquid chromatography separates proteins according to charge
381
What is sickle cell trait?
- HbAS
- Normal life expectancy
- Normal blood count
- Usually asymptomatic
- Rarely painless haematuria
- Caution: anaesthetic, high altitude, extreme exertion
382
How does sickle Hb affect red cells?
Makes them less deformable
383
What does each haemoglobin molecule contain?
- Four globin protein chains
- Four haem groups
- Four molecules of iron
- Up to 4 molecules of oxygen
384
What are the different types of globin proteins?
- Alpha globin chains
- Beta globin chains
- Gamma globin chains
- Delta globin chains
385
What is most adult haemoglobin?
HbA
| - Made up of two alpha and two beta chains
386
What is HbA2 made up of ?
2 alpha
| 2 delta
387
Which form of haemoglobin has the highest affinity for oxygen?
A) Hb with three oxygens in the relaxed configuration
B) Hb with no oxygens in the tight configuration
A haemoglobin with 3 oxygens in the relaxed form would have a higher affinity than a haemoglobin molecule with zero oxygens in the tight form
388
Describe the affinity of deoxyhaemoglobin for oxygen
- Low affinity therefore will only take up oxygen if the oxygen saturation is very high e.g. in the lungs
- It will not pick up oxygen in metabolically active tissues where oxygen tensions are low and oxygen is needed by the tissue
389
Describe the affinity of oxyhaemoglobin for oxygen
- High affinity for oxygen
- It will not release oxygen easily
- It will only give up oxygen in tissues where there is no oxygen around
390
What molecule makes haemoglobin less flexible?
2,3 BPG as it forms extra bonds
- As more oxygen molecules, the tight form flips into the relaxed form and the relaxed form can accommodate more oxygens because there is more space
391
What factors stabilise the deoxy Hb molecule and decrease its affinity for oxygen?
Increased 2,3 BPG and H+ ions and C02 (Bohr effect)
| - Shifts the dissociation curve to the right
392
How many alpha genes are there for the alpha globin protein?
2
- 2 from each parents
- Adults have a totaly of four alpha globin genes
393
How do globin genes occur?
In clusters
394
From when is haemoglobin made in the bone marrow?
4-5 months prenatally
| - Before this it is made in the liver and prior to this it is made in the yolk sac
395
From when is alpha globin made?
In the foetus from 3 months and continues to be made throughout adult life
- Before this, there is an embryonic alpha type globin
396
From when is beta globin made?
Appreciable quantities from 4-5 months post-natally.
| prior to this there is foetal haemoglobin and before this there is an embronic variant
397
Where is the alpha cluster found?
Chromosome 16
| - Contains two alpha genes plus an embryonic gene and some pseudogenes
398
Where is the beta cluster found?
Chromosome 11
| - Contains beta genes, delta genes and gamma genes
399
What is the consequence of there being different globin genes?
There are various types of Hb that are possible (6 common variants)
- Some combinations do not occur: there must be a pair from the alpha cluster and beta cluster separately
400
What are thalassaemias?
- Disorders in which there is reduced production of one of the two types of globin chain in Haemoglobin which leads to imbalanced globin chain synthesis
- 5% of world population estimated to be carriers
401
What is severe alpha thalassaemia?
Loss of three or four alpha chains
1) Three alphas missing is called Haemoglobin H
- Need life long transfusions
2) Four alphas missing is fatal in utero and it called Haemoglobin Barts
402
What is Thalassaemia major?
A severe defect in BOTH beta chains
- No problems in utero because HbF is alpha and gamma chains
- At 2-3 months, become profoundly anaemic with Hb 3 or 4g/dl
- Need life long transfusions
403
What are the features of thalassaemia trait
- May be mildly anaemic but can be normal
- Usually have a low MCV and low MCH
- Haemoglobin electrophoresis will identify a rise in HbA2 relative to HbA which occurs in beta thalassaemia trait
- Beta chains are reduced but delta chains are okay
404
Why do we need to diagnose haemoglobinopathies?
- Confirm possible diagnosis
- Investigate anaemia with a low MCV
- Permit genetic counselling - antenatal screening
- Neonatal screening of at risk neonates
405
How do thalassaemias arise?
Globin genes are transcribed into messenger RNA which is processed before translation into a protein
406
What might reduction of globin chains result from?
1) Gene missing completely (deletion)
2) Gene abnormal
a) Start signal gone- no transcription
b) mRNA unstable- no translation
c) protein abnormal/dysfunctional
407
What are the causes of alpha thalassaemia?
- Gene deletion
- Co-incidental finding
- Occasional sig anaemia
- Death in utero rare
408
What are the causes of beta thalassaemia?
- Point mutation
- Co-incidental finding
- Thalassaemia major severe life long anaemia
409
What may problems start in utero in alpha thalassaemia?
Alpha globin chains are found in HbF
410
What are the possible alpha thalassaemia syndromes?
alpha+ trait: Where one locus fails to function. Mild anaemia
alpha 0 trait: where two loci on the same chromosome are dysfunctional. Mild anaemia (low MCH)
Haemoglobin H= Disease with 3 loci affected. Significant anaemia.
Haemoglobin Bart's: hydrops fetalis where all four loci are defective and death in utero is the norm
411
Why is antenatal screening important to identify alpha0 in pregnant women?
- If a pregnant lady has two alphas missing it is important to investigate her partner. If he has two alphas missing then they should be counselled about the risks of an affected child and offered antenatal diagnosis if they would consider a termination.
412
How is alpha0 identified?
- Low MCH
413
What is the genetic background of beta thalassaemia?
Point mutations
414
What is the pathogenesis of beta thalassaemia?
- 1) No beta chains
2) Alpha chains form tetramers, alpha4
- Precipitate in bone marrow
- Enter circulation and removed in spleen
415
How can carriers for abnormal beta globin gene be identified?
Beta thalassaemia trait
- Hb may be normal
- MCV low
- MCH low
- Red cell count increased
- HbA2 increased (electrophoresis)
416
How does thalassaemia major present within the first year of life?
- Profound anaemia
- Failure to thrive
- Malaise
- Splenomegaly
417
What are the clinical features of beta thalassaemia?
```
1) Death of red cells in marrow
'ineffective erythropoiesis'
2) Removal of red cells by spleen
- Large spleen
- Anaemia
- Increased eryhtropoietin
- Expansion of bone marrow
```
418
What is the course of thalassaemia major?
No transfusions- die aged 7
| Blood transfusions- die aged 25 from iron overload and viral transmission
419
How much iron is in the blood?
200mg in each unit
420
Where and why does iron accumulate?
```
Liver- cirrhosis
Heart- cardiac failure
Endocrine glands:
Pancreas- diabetes
Pituitary- hypogonadism
Thyroid- hypothyroid
```
421
How is iron overload managed?
Remove with desferrioxamine (DFO)
422
What are the problems with desferrioxamine?
- Not orally active
- Subcutaneous infusion
- Expensive
423
What are the pros of stem cell transplantation?
- No transfusions
- No desferrioxamine (DFO)
- Growth is normal
424
What are the cons of stem cell transplantation?
1) Transplant associated mortality
2) Infertility due to stem cell transplant
3) Some patients will still get an iron overload
425
When is a stem cell transplantation not so useful?
- Poor chelation
| - Liver large or evidence of fibrosis on biopsy
