Haematology Flashcards
(138 cards)
1
Q
What is the defining characteristic of a stem cell?
A
Stem cells can self-renew as they have the ability to divide into 2 cells with different characteristics: one another stem cell; the other capable of differentiating to mature progeny.
2
Q
Normal erythropoiesis requires erythropoietin. Where are the endogenous erythropoietin production sites?
A
90% from juxtatubular interstitial cells in the kidney in response to hypoxia.
10% from hepatocytes.
3
Q
Briefly name the key cells in erythropoiesis.
A
Myeloid stem cell –> proerythroblast –> erythroblast –> erythrocyte.
4
Q
Name some cytokines required in the production of granulocytes and monocytes.
A
G-CSF (granulocyte colony-stimulating factor); GM-CSF (granulocyte-macrophage colony-stimulating factor); M-CSF (macrophage colony-stimulating factor) and various interleukins.
5
Q
What are granulocytes?
A
A category of leukocytes with granules in their cytoplasm (e.g. neutrophil, basophil, eosinophil).
6
Q
Briefly describe the function of platelets.
A
They survive around 10 days in circulation and have a role in primary haemostasis. They contribute phospholipid, which promotes blood coagulation.
7
Q
Define anisocytosis and poikilocytosis.
A
Anisocytosis is where erythrocytes show more variation in size than is normal.
Poikilocytosis is where erythrocytes show more variation in shape than is normal.
8
Q
What is a microcyte?
A
An erythrocyte which is smaller than normal. A blood sample shows MICROCYTOSIS. Contrasts with macrocytosis and macrocytes.
9
Q
Why do normal erythrocytes have a central pallor which extends roughly 1/3 of the diameter?
A
Due to the disc shape of the erythrocyte which means there is less haemoglobin in the centre.
10
Q
Define hypochromia.
A
Erythrocytes with a larger area of central pallor than normal, due to less haemoglobin or a flatter cell. These cells are described as hypochromic and are often microcytic.
11
Q
Define hyperchromia.
A
Erythrocytes which lack central pallor, because they’re thicker than normal or because their shape is abnormal. Described as hyperchromic or hyperchromatic.
12
Q
What are the two most important types of hyperchromic erythrocytes?
A
Spherocytes: cells approximately spherical in shape. These result from the loss of cell membrane without the equivalent loss of cytoplasm.
Irregularly contracted cells are irregular in outline but smaller than normal cells. Usually result from oxidant damage to the cell membrane and the haemoglobin (e.g. in glucose-6-phosphate deficiency).
13
Q
How can you detect young erythrocytes on blood films?
A
Look out for polychromic cells. Polychromasia describes an increased blue tinge to the cytoplasm of the erythrocyte, indicating the cell is young.
Do a reticulocyte stain. Exposes living erythrocytes to methylene blue which precipitates as a network or “reticulum”. Identification of reticulocytes more reliable for counting than polychromasia.
14
Q
Give 6 types of poikilocytes.
A
Fragments (schistocytes), spherocytes, irregularly contracted cells, sickle cells, target cells and elliptocytes.
15
Q
Describe target cells.
A
Cells with an accumulation of haemoglobin in the centre of the area of central pallor. They occur in obstructive jaundice, liver disease, haemoglobinopathies and hyposplenism.
16
Q
What can cause the presence of elliptocytes?
A
Hereditary elliptocytosis or iron deficiency.
17
Q
Contrast rouleaux and agglutinates.
A
Rouleaux are stacks of red cells, which resemble piles of coins, resulting from alterations in plasma proteins.
Agglutinates are irregular stacks rather than tidy stacks, usually resulting from antibody on the surface.
18
Q
What is a Howell-Jolly body?
A
A nuclear remnant in an erythrocyte. Commonest cause is a lack of splenic function.
19
Q
Define leucocytosis and leucopenia and neutrophilia and neutropenia.
A
Leucocytosis is too many leucocytes.
Leucopenia is too few leucocytes.
Neutrophilia is too many neutrophils.
Neutropenia is too few neutrophils.
20
Q
What is left shift on a blood film?
A
An increase in non-segmented neutrophils (band cells) or that there are neutrophil precursors in the blood.
21
Q
What are the causes of toxic granulation (heavy granulation of neutrophils)?
What causes vacuolation?
A
Infection, inflammation and tissue damage.
Normal feature of pregnancy.
Vacuolation = bacterial infection
22
Q
Define hypersegmented neutrophil and give possible causes.
A
An increase in the average number of neutrophil lobes or segments. Causes include a lack of vitamin B12 or folic acid.
23
Q
How is a reference range derived and how can it be enumerated from a normal distribution?
A
A reference range is derived from a carefully defined reference population. Samples are collected from healthy volunteers with defined characteristics. Data with a normal distribution can be analysed by determining the mean and standard deviation and taking the mean +/- 2SD as the 95% range.
24
Q
What is in a full blood count (FBC)?
A
White blood cell count (x10^9/l) Red blood cell count (x10^12/l) Platelet count (x10^9/l) Hb (haemoglobin concentration) (g/l) Hct (haematocrit) (l/l or %) MCV (mean cell volume) (fl) MCH (mean cell haemoglobin) (pg) MCHC (mean cell haemoglobin concentration (g/l)
25
How are white blood cell, red blood cell and platelet counts done?
By automated instruments which enumerate electronic impulses generated when cells flow between a light source and a sensor or when cells flow through an electric field.
26
How is haemoglobin concentration and haematocrit measured?
By an automated instrument which converts Hb to a stable form and measures light absorption at a specific wavelength.
Haematocrit is measured by centrifuging a blood sample.
27
How are MCV, MCH and MCHC calculated?
```
MCV = Hct / RBC (divide the total volume by number)
MCH = Hb / RBC (amount of Hb in given volume of blood by number of cells)
MCHC = Hb / Hct (amount of Hb in a given volume of blood by the proportion of the sample represented by erythrocytes).
```
28
In terms of MCHC, what does hypochromia indicate?
A low MCHC (hypochromia correlates with MCHC).
29
What components of a FBC would be raised in a subject with polycythaemia?
Haemoglobin concentration, red blood cell count and haematocrit are all increased compared with normal subjects of the same age and gender.
30
What is the cause of pseudopolycythaemia?
A reduced plasma volume.
31
What are the causes of true polycythaemia?
Inappropriately (tumour) or appropriately (hypoxia) raised erythropoietin levels.
Blood doping or over-transfusion.
Administering erythropoietin.
Polycythaemia vera.
32
What is polycythaemia vera?
An erythropoietin independent polycythaemia caused by an intrinsic bone marrow disorder. Can lead to hyperviscosity (thick blood), which can lead to vascular obstruction.
33
How can you treat polycythaemia?
If there is no physiological need for high haemoglobin concertation, or if the hyperviscosity is extreme, blood can be removed to thin the blood. If there's an intrinsic bone marrow disease, drugs can be used to reduce bone marrow production of red cells.
34
What are the main mechanisms of anaemia?
Reduced production of erythrocytes/ haemoglobin in the bone marrow, loss of blood, reduced survival of erythrocytes, pooling of RBCs in an extra-large spleen.
35
What are the commonest causes of microcytic anaemia?
Defect in haem synthesis: iron deficiency.
Defect in globin synthesis (thalassaemia) - either A or B thalassaemia depending upon whether it is the A or B chain which is affected.
ACD.
36
Give mechanisms behind major causes of macrocytic anaemia.
Abnormal haemopoiesis: red cell precursors continue to make Hb and other proteins but fail to divide normally. Eg megaloblastic erythropoiesis which refers to a delay in maturation of the nucleus while the cytoplasm continues to grow.
Premature release of cells from bone marrow as young red cells are around 20% larger - for example a recent major blood loss with adequate iron stores would cause reticulocyte release.
37
Give mechanisms of normocytic anaemia.
Recent blood loss, failure in RBC production, pooling in spleen.
38
What is haemolytic anaemia?
Anaemia resulting from shortened survival of erythrocytes in circulation. Can result from intrinsic abnormalities of RBCs or extrinsic factors affecting them.
39
Contrast intravascular and extravascular haemolysis.
Intravascular haemolysis occurs if there's very acute damage to the erythrocyte.
Extravascular haemolysis occurs when defective red cells are removed by the spleen.
40
When would you suspect haemolytic anaemia?
Otherwise unexplained, normochromic and normocytic or macrocytic anaemia.
Evidence of morphologically abnormal erythrocytes,
Evidence of increased RBC breakdown or increased bone marrow activity.
41
Give inherited causes of haemolytic anaemia.
```
Hereditary spherocytosis (affects membrane).
Sickle cell anaemia (affects the Hb)
Pyruvate kinase deficiency (affects the glycolytic pathway)
Glucose-6-phosphate deficiency (affects the pentose shunt, renders the erythrocytes susceptible to oxidant damage).
```
42
Give acquired causes of haemolytic anaemia.
Autoimmune haemolytic anaemia - attacks membrane.
Drugs and chemical (oxidants).
Microangiopathic haemolytic anaemia (leads to schistocytes).
Malaria.
43
Detail inherited spherocytosis.
A hereditary defect in the cell membrane which causes the cell to have part of its membrane removed in the spleen. This means the RBCs become less flexible and are then removed prematurely by the spleen (extravascular haemolysis). The bone marrow responds by increasing output, causing polychromasia and reticulocytosis. The increased Hb breakdown causes bilirubin to build up, causing jaundice and gall stones. The only effective treatment is splenectomy. A good diet/ a daily folic acid tablet is needed to prevent secondary folic acid deficiency.
44
Detail glucose-6-phosphate dehydrogenase (G6PD) deficiency.
G6PD is important in the protection of erythrocytes against oxidant damage. Oxidants may be generated in the blood (in infection) or may be exogenous. Usually results in severe intravascular haemolysis (as a result of infection or exposure to exogenous agents). These episodes are associated with considerable numbers of irregularly contracted cells. Also associated with Heinz bodies: round inclusions containing denatured haemoglobin. May require blood transfusion.
45
What are Heinz bodies?
Structures formed in glucose-6-phosphate dehydrogenase deficiency when erythrocytes are exposed to oxidants. They are round inclusions formed as haemoglobin denatures, which leave defects in the erythrocytes.
46
Detail autoimmune haemolytic anaemia.
Autoantibodies directed against RBC antigens. The immunoglobulin bound to the RBC is recognised by splenic macrophages, which remove parts of the cell membrane, leading to spherocytosis. This makes the erythrocytes less flexible. The combination of cell rigidity and recognition of antibody + complement on RBC surface leads to removal by spleen. Treatment included immunosuppressives and splenectomy if severe. Diagnosis involves the presence of spherocytes, detection of Ig + complement and the detection of autoantibodies.
47
Where is haem synthesised? Where are globin chains synthesised?
Haem is synthesised in mitochondria.
| Globin is synthesised in ribosomes.
48
What are the globin chains in HbA, HbA2 and HbF?
```
HbA = A2B2
HbA2 = A2D2
HbF = A2Gamma2
```
49
Describe the primary, secondary and tertiary globin structure.
Primary: A = 141AA, non-A = 146AA.
Secondary: 75% helical arrangement
Tertiary: approximate sphere, hydrophilic surface, hydrophobic core, haem pocket.
50
What factors cause a right-shift in the haemoglobin-oxygen dissociation curve?
An increase in 2,3-DPG concentration, proton concentration (a decrease in pH), CO2 and HbS.
51
What is thalassaemia and what are its causes and inheritance patterns?
Thalassaemia is caused by defects in globin chain synthesis leading to reduced of absent production of the affected chain. It is classified based on the globin type affected.
It is also classified by severity: minor "trait", intermedia (transfusion independent), major (transfusion dependent).
It follows an autosomal recessive mendelian inheritance.
Inheritance of 2B^0 genes gives rise to a major classification due to absence of synthesis. 2B^+ gives rise to an intermedia classification due to reduced synthesis,
52
What would the FBC and blood film of a patient with thalassaemia look like?
Thalassaemia leads to a microcytic, hypochromic blood picture IN THE ABSENCE OF IRON DEFICIENCY.
The RBC count is raised relative to Hb.
Target cells present with poikilocytosis but no anisocytosis.
In B-thalassaemia, HbA2 and HbF are raised.
In A-thalassaemia, HbA2 and HbF are normal, so you must make a presumptive diagnosis followed up with DNA analysis.
53
Describe the presentation and blood film of a patient with beta thalassaemia major.
Severe anaemia - incompatible with life without regular blood transfusions. Clinical presentation usually after 4-6 months of life. Hepatosplenomegaly due to extra-medullary haematopoiesis. Erythroid hyperplasia in bone marrow.
Blood film shows gross hypochromia, with microcytic erythrocytes and poikilocytosis (with target cells).
HbA2 and HbF raised.
54
What are the clinical features of B thalassaemia?
Chronic fatigue, failure to thrive, jaundice, delay in growth and puberty, skeletal deformity, splenomegaly, iron overload, cardiac failure.
55
Describe the treatment available for B thalassaemia sufferers.
Transfusions with phenotyped RBCs. Requires regular transfusions 2-4 weekly.
Iron chelation therapy: starts after 10-12 transfusions or when serum ferritin >1000mcg/l (iron accumulates due to repeated transfusions)
56
What is the genetic cause of sickle cell disease?
A missense mutation at codon 6 of gene for the B-globin chain. Causes a change from GLUTAMIC ACID, a polar (soluble) amino acid to VALINE, a non-polar (insoluble amino acid).
57
Define sickle cell disease (SCD)
A term which incorporates sickle cell anaemia (homozygous SS) and all other conditions that can lead to a disease syndrome due to sickling, such as SC, SB thalassaemia.
58
What are the causes of anaemia in sickle cell anaemia.
Haemolysis due to defective Hb.
Also, a reduce erythropoietic drive as HbS is a low affinity haemoglobin (low affinity for oxygen) which readily releases oxygen in the JGA reducing erythropoietin production.
59
Describe the vascular complications arising in sickle cell anaemia.
Microvascular occlusion due to sickled cells adhering to vascular endothelium. Leads to tissue damage and necrosis (infarction), pain and dysfunction.
Intravascular haemolysis leads to cell-free haemoglobin in the vessels. Cell-free Hb scavenges NO (a potent vasodilator) limiting NO bioavailability. Leads to HYPERTENSION. Pulmonary hypertension is correlated with the severity of haemolysis.
60
Why does sickle cell disease not appear in the first few months of life and what are the early symptoms?
Symptoms are rare before 3-6months due to the abundance of HbF. Onset coincides with the switch from foetal to adult haemoglobin synthesis.
Early manifestations include dactylitis, splenic sequestration and infection.
61
What is uncommon about stroke patients with sickle cell disease?
The most common age is 2-9 years.
| Affects major cerebral arteries.
62
What are the lab features of someone's blood with sickle cell disease?
Low haemoglobin concentration.
High reticulocyte concentration.
On film: sickled-cells, boat cells, target cells, Howell-Jolly bodies.
63
What is the solubility test in SCD and what technique gives a definitive diagnosis?
Solubility test: in the presence of a reducing agent, oxyHb converted to deoxyHb. Solubility decreases, solution becomes turbid in sickle cell disease. Doesn't differentiate AS/SS.
A definitive diagnosis can be achieved via haemoglobin electrophoresis.
64
Describe disease-modifying therapies in SCD.
Exchange transfusion.
HSCT - survival 90-95%; curative 85-90%
Induction of HbF - hydroxyurea (hydroxycarbamide).
HbF inhibits polymerisation of HbS. Patients with higher HbF levels have fewer complications and improved survival. Decreases "stickiness" of sickled RBCs. Reduces WBC production. Improves hydration of RBCs. Generates NO which improves blood flow.
65
Describe sickle cell trait (HbAS).
Normal life expectancy. Normal blood count. Usually asymptomatic. Rarely painless haematuria.
Caution: avoid hypoxia (high altitude, extreme exertion).
66
List possible causes of leucocytosis.
```
Reactive causes (infection, inflammation).
Malignant causes (leukaemia)
Failure of apoptosis.
```
67
List possible causes of leucopenia.
Impaired bone marrow function (B12 / folate deficiency)
Bone marrow failure (cancer, past chemotherapy, aplastic anaemia).
Reduced cell survival, e.g. immune breakdown.
68
Describe the time-span that neutrophilia can develop in.
Minutes (in demargination) - since 50% of neutrophils are marginated.
Hours in the case of early release from the bone marrow
Days in the case of increased production (e.g. infection)
69
Give an overview of a vessel's response to injury.
Vessel constriction (contraction of vascular SM) to limit blood flow.
Formation of an unstable platelet plug. Adhesion and aggregation of platelets to limit blood loss and provide surfaces for coagulation.
Stabilisation of the plug with fibrin to stop blood loss.
Vessel repair and dissolution of the clot. Restores vessel integrity.
70
Describe platelets.
Small (2-4 micrometres) anucelar cells with lifespans of roughly 10 days. Derived from megakaryocytes in bone marrow, each of which can produce roughly 4000 platelets. Have lots of adhesive receptors.
71
Describe primary haemostasis.
vWF binds to collagen and the blood's shear forces stretches it out, exposing binding sites for platelets. Platelets bind to vWF via Gp1b.
Platelets bind to collagen via Gp1a (low flow conditions).
Platelets release ADP and thromboxane (TXA2) from granules, stimulating other platelets. TXA2 causes GpIIb/IIIa expression allowing platelets to bind to each other via FIBRINOGEN (and Ca2+).
PRIMARY HAEMOSTATIC PLUG.
72
What is a Gla domain?
A domain which contains many glutamic acids (Glu) which can be converted to gamma-carboxyglutamic acid (Gla) by vitamin K carboxylase. This gives these residues affinity for Ca2+. Ca2+ causes them to fold up into a conformation which allows binding to negatively charged phospholipids.
73
Which clotting factors are Gla domain containing proteins?
FVII, FIX, FX, prothrombin (FII), protein C and protein S.
74
How does warfarin work?
It is a vitamin K antagonist, inhibiting the action of vitamin K carboxylase. Hence, Gla domain containing proteins can't bind to phospholipids.
"Inhibits vitamin K dependent synthesis of biologically active forms of calcium dependent clotting factors".
75
Describe extrinsic coagulation.
TF + FVII associate via Gla domain.
Cause FIX and FX to be converted to FIXa and FXa respectively.
FXa causes prothrombin (FII) to be converted to thrombin. This is inefficient (small quantities).
Thrombin converts FVIII and FV to FVIIIa and FVa respectively.
FVIIIa is a cofactor of FIXa. This complex (with Ca2+) produces FXa much more efficiently than TF-FVIIa.
FXa and FVa (with Ca2+) produce thrombin 300,000 times more efficiently than FXa alone.
Thrombin results in the conversion of fibrinogen to fibrin. FIBRIN MESH.
76
Describe how tissue factor pathway inhibitor (TFPI) works.
TFPI has 3 kunitz domains.
The 2nd Kunitz domain binds to FXa.
K1 binds to TF-FVIIa complex.
Locks all 4 proteins in an inactive form.
77
What is antithrombin?
```
A SERPIN (serine protease inhibitor) - inactivates FXa, thrombin, FXIIa, FIXa, FXIa. "Mops up" free serine proteases which escape the site of vessel damage.
Heparin is a cofactor which enhances the efficiency of antithrombin.
```
78
Which coagulation factors are serine proteases?
FVII, FXI, FIX, FX, FII (prothrombin) and protein C.
79
Describe indirect inhibition of coagulation.
Protein C is activated by a thrombin-thrombomodulin complex. Activated protein C inhibits thrombin generation by proteolytically inactivating FVa and FVIII a.
Protein C is activated at the edge of a clot as thrombomodulin is on intact endothelium.
80
Describe fibrinolysis.
Tissue plasminogen factor (tPA) and plasminogen meet on fibrin. Plasminogen is converted to PLASMIN, which targets fibrin. Breaks down fibrin to form fibrin degradation products.
Regulated by antiplasmin.
81
Give causes of thrombocytopenia, a cause of primary haemostasis failure.
Bone marrow failure e.g. leukaemia/ B12 deficiency
Accelerated clearance e.g. immune thrombocytopenia (ITP), DIC.
Increased pooling of platelets in spleen (hypersplenism).
Impaired function: hereditary absence of glycoproteins or storage granules, or acquired due to drugs such as aspirin.
82
Describe von Willebrand disease (vWD).
Hereditary (autosomal dominant) - most common bleeding disorder. Acquired is rare.
Deficiency = type 1
Abnormal function = type 2
Absence = type 3
83
Describe typical bleeding in a primary haemostatic disorder.
Immediate, prolonged from cuts, epistaxis, gum bleeding, menorrhagia, easy bruising, prolonged bleeding after trauma or surgery, superficial bleeding.
84
What physical feature is characteristics of thrombocytopenia?
Petechiae (spots). SEE IMAGES.
85
What tests can you perform to detect primary haemostatic disorders?
Measure platelet count, look at platelet morphology.
Bleeding time (PFA100 in lab).
Assays of vWF.
86
Describe different types of inherited coagulation factor deficiencies.
Factor deficiencies are VERY different.
Haemophilia A is no FVIII, B is no FIX. Both lead to no thrombin burst and insufficient fibrin. X-linked inheritance, compatible with life.
All other deficiencies are autosomal recessive and hence much rarer.
FII deficiency incompatible with life.
FXI = bleed after trauma (not spontaneously).
FXII = no excess bleeding at all.
87
What are acquired causes of factor deficiency?
Liver disease (all factors, except FVIII, made in liver), dilution (people on transfusion), anticoagulant drugs.
88
What is disseminated intravascular coagulation (DIC)?
Sepsis (usually) causes activation of TF inside vasculature - leading to unregulated activation of coagulation. Activation of fibrinolysis depletes fibrinogen. Consumes and depletes coagulation factors and platelets.
Consequences: widespread bleeding. Deposition of fibrin in vessels causes organ failure.
89
How do you treat DIC?
Support by providing replacement factors.
| Treat the cause (e.g. treat the infection in sepsis).
90
Describe typical bleeding in a secondary haemostatic disorder.
Superficial cuts don't bleed. Bruising common. Bleed into joints (haemarthrosis). Delayed bleeding which stops and then restarts.
91
Describe the 2 clotting screen tests.
```
Prothrombin time (PT) - looks at extrinsic pathway (VIIa, IXa, Xa, IIa).
Activated partial thromboplastin time (APTT) - looks at intrinsic pathway (XIIa, XIa, VIIIa, IXa, Va, Xa, IIa).
In both cases, measuring time for the first strands of fibrin to appear.
```
92
Describe defects in fibrinolysis.
```
Hereditary = antiplasmin deficiency.
Acquired = drugs such as tPA (alteplase is a recombinant tissue-type plasminogen activator (rt-PA)), and DIC.
```
93
Suggest treatments for haemostatic disorders.
Failure of production/function: replace missing factor, stop drugs.
Immune destruction: immunosuppression, splenectomy for ITP.
Increased consumption: treat causes, replace as necessary.
94
How is desmopressin (DDAVP) useful in treating type 1 vWD.
Vasopressin causes endothelial cells to release vWF - hence desmopressin also does this.
95
What is tranexamic acid useful for?
It competes with fibrin for binding of tPA, and hence is anti-fibrinolytic.
96
Describe abnormal bleeding.
Spontaneous, out of proportion to the trauma, unduly prolonged, restarts after appearing to stop.
97
What can cause defective or deficient collagen, a problem in primary haemostasis?
Steroid therapy, age, scurvy.
98
Define thrombosis.
Intravascular coagulation. Thrombi may be venous or arterial.
99
What symptoms present from venous and arterial thrombi?
Artery: MI, stroke, limb ischaemia,
Vein: pain and swelling.
100
Give disorders of thrombosis.
Deficiency of anticoagulant proteins (protein C, protein S).
Factor V leiden (increased activity due to FVa protein C resistance).
Thrombocytosis (increased platelets).
101
What are Vit B12 and folic acid needed for?
Vitamin B12 needed for DNA synthesis and integrity of the nervous system.
Folic acid is required for DNA synthesis and homocysteine metabolism.
102
Which cells are affected by vitamin B12 and folate deficiencies and what symptoms result from this?
All rapidly dividing cells are affected: bone marrow, epithelial cells of mouth and gut, gonads and embryos.
Consequences: weak, tired, SoB, jaundiced due to anaemia. Weight loss, change in bowel habit and sterility.
103
What are the causes of macrocytic anaemia?
Macrocytic: average RBC size above reference range.
| Causes include B12/folate deficiency, liver disease/ alcohol, hypothyroidism, drugs and haem disorders.
104
What is the characteristic anaemia caused by B12/folate deficiency.
Macrocytic and megaloblastic anaemia.
Megaloblastic describes a morphological change in the red cell precursors in the bone marrow. There is asynchronous maturation of the nucleus and cytoplasm in the erythroid series. Normally, the nucleus condenses and disappears and the cytoplasm becomes more and more pink.
In peripheral blood, you see anisocytosis, large red cells, hypersegmented neutrophils.
Hypersegmented neutrophil indicative of B12/folate deficiency.
105
Which tests should you conduct upon finding macrocytosis?
Liver function tests, thyroid function tests, reticulocyte count.
106
Where do you get dietary folate and what conditions of increased demand lead to deficiency.
Folate found in fresh, leafy vegetables. Destroyed by overcooking and processing.
Increased demand: pregnancy, adolescence, premature babies, malignancy, erythroderma, haemolytic anaemias.
107
What vascular problems are very high homocysteine levels (due to folate deficiency) associated with?
Atherosclerosis and premature vascular disease.
108
How is folate deficiency prevented in pregnancy?
All pregnant women take 0.4mg folic acid prior to conception and first 12 weeks.
109
What are some consequences of B12 deficiency?
Neurological problems: dementia, optic atrophy, bilateral peripheral neuropathy, subacute combined degeneration of the cord.
History: paraesthesia (pins and needles), muscle weakness, difficulty walking, visual impairment, psychiatric disturbance.
110
What can cause B12 deficiency?
Veganism - since B12 is found in animal produce. However, the liver has stores which last 3-4 years.
Poor absorption. Must bind with intrinsic factor from stomach parietal cells, which then binds to ileal receptors.
Hence, post-gastrectomy, gastric atrophy, antibodies to IF or parietal cells can all cause a deficiency.
111
What is pernicious anaemia?
An autoimmune condition associated with severe lack of IF. Peak age 60. IF antibodies occasionally found in other conditions. 90% of time when parietal cell antibodies found is pernicious anaemia.
Pernicious anaemia is a type of megaloblastic anaemia.
112
Describe the basis of the shilling test.
Prior to shilling test, replenish B12 stores. Drink radiolabelled B12 and measure excretion in the urine.
If no B12, not absorbing B12 (pernicious anaemia/ small bowel disease), or hadn't corrected deficiency before test.
Then part 2 where you repeat with IF. Measure B12 in urine again. Differentiates between pernicious anaemia and small bowel disease.
113
How much iron is needed every day and where do we get it from?
Need 20mg/day. Iron is recycled, but some is lost due to desquamated cells of skin and gut, and bleeding (e.g. menstruation). Men therefore need 1mg a day and women need 2mg a day.
Human diet provides 12-15mg of iron a day, with it occurring in most natural foods (meat and fish as haem, vegetables, whole grain cereal, chocolate). However, most eaten iron is not absorbed, you can only absorb ferrous iron. Orange juice helps.
114
Briefly describe how high plasma Fe2+ levels affects absorption.
High iron leads to high hepcidin.
| Hepcidin inhibits ferroportin, reducing absorption.
115
What are transferrin saturation and total iron binding capacity?
Transferrin saturation is the proportion of transferrin in the plasma which is associated with Fe2+ - usually 20-50%.
Total iron binding capacity (TIBC) is the amount of transferrin in the blood.
116
Describe anaemia of chronic disease (ACD)?
A condition where there is no obvious cause of the anaemia except they're ill.
Lab signs of being ill: increased c-reactive protein, increased erythrocyte sedimentation rate (ESR), increases in ferritin, FVIII, fibrinogen and immunoglobulins.
Associated conditions: chronic infections (HIV, TB), chronic inflammation (rheumatoid arthritis), malignancy, cardiac failure.
Cytokines prevent the usual flow of iron from duodenum to red cells:
Cytokines stop erythropoietin increasing, stop iron flowing out of cells (increased FERRITIN), increase death of red cells.
117
Give causes of iron deficiency.
Bleeding (e.g. GI, heavy periods).
Increased use (growth/ pregnancy).
Dietary deficiency (vegetarianism).
Malabsorption (coeliac disease).
118
If you have a patient with iron deficiency, who has a good diet and no coeliac antibodies, is male (or female over 40) what would you do?
Full GI investigation.
| Upper GI endoscopy, duodenal biopsy, colonoscopy.
119
What are the 3 main causes of microcytic anaemia?
Iron deficiency, ACD, thalassaemia trait.
120
How would you rule out thalassaemia trait as a differential when you find microcytic anaemia? How could you confirm the diagnosis?
Test serum iron - low in ACD and iron deficiency but NORMAL in thalassaemia trait.
Confirm with haemoglobin electrophoresis.
121
What would a microcytic anaemia with low ferritin tell you about its cause? Why would it be problematic if ferritin was normal in the presence of microcytic anaemia?
Low ferritin = iron deficiency
Ferritin is raised with ACD.
However, if you have both ACD and iron deficiency, ferritin can be normal. Further investigation needed.
122
How is transferrin affected by ACD and iron deficiency?
Transferrin increases in iron deficiency.
| Normal or even low in ACD.
123
How is transferrin saturation affected by ACD and iron deficiency?
Transferrin saturation low in iron deficiency.
| Normal in ACD.
124
Summarise blood finding in differentials for microcytic anaemia.
Iron deficiency: Hb low, MCV low, serum iron low, ferritin low, transferrin high, transferrin saturation low.
ACD: Hb low, MCV low/ (normal), serum iron low, ferritin high (normal), transferrin normal (low), transferrin saturation normal.
Thalassaemia trait: Hb low, MCV low, serum iron normal, ferritin normal, transferrin normal, transferrin saturation normal.
125
Describe the ABO classification of blood type.
A and B antigens on red cells formed by adding one or other sugar residue onto a common glycoprotein and fucose stem on red cell membrane.
O had neither A nor B sugars: fucose stem only.
A gene codes for enzyme which adds N-acetyl galactosamine to stem.
B gene codes for enzyme which adds galactose.
126
How can you check someone's blood type is compatible?
A person has IgM against any antigen not present on own red cells.
Cross-match: mix patient's serum (IgMs) with donor red cells - shouldn't react (clump and descend in tube).
127
What are RH groups?
Blood groups: RhD positive if have D antigen. RhD negative if doesn't have D antigen.
D = antigen, d = no antigen (recessive).
Don't naturally have the anti-D antibody (unlike ABO), made after first exposure.
85% of people are RhD positive.
128
What is an O+ blood group?
ABO group O (absence of A and B antigens) and RhD positive.
129
What exposures lead RhD negative people to make anti-D antibodies?
Exposure via transfusion or pregnant women can be exposed by a RhD+ foetus.
After exposure, patient must receive RhD- blood.
130
What is haemolytic disease of the newborn (HDN)?
If RhD- mother makes anti-D and in next pregnancy, foetus is RhD+, mother's IgG antibodies can cross placenta and cause haemolysis of foetal red cells, causing death in severe cases.
131
Why are whole units of blood not routinely given?
More efficient, some components degrade quicker and avoids fluid overload if patient doesn't need plasma.
132
How is a unit of blood separated?
Centrifuged: red cells bottom, platelets middle and plasma top. Each layer is squeezed into a satellite bag and cut free (it is a closed system).
Plasma can be used as fresh frozen plasma (FFP), cryoprecipitate or plasma for fractionation.
133
Describe a unit of red cells from 1 donor.
Shelf-life of 5 weeks, stored at 4 degrees (fridge).
Given through blood-giving set which filters to remove clumps/ debris.
Rarely need frozen red cells (National Frozen Bank) - for rare groups. Poor recovery on thawing (lose up to 1/3 of RBCs).
134
Describe FFP.
1 unit from 1 donor - stored at -30 (within 6 hours).
Shelf-life up to 3 years.
Must thaw approx. 20-30mins and can't thaw above body temp.
Given if bleeding and abnormal coagulation results.
Reversal of warfarin for urgent surgery etc.
135
What is cryoprecipitate used for?
From FFP thawed at 4-8 degrees overnight. Contains fibrinogen and FVIII. Same as FFP (3years, -30) - given for massive bleeding and low fibrinogen.
136
Describe how we obtain and store platelets.
1 pool from 4 donors or from 1 donor by apheresis.
Stored at 22 and constantly agitated. Shelf life of only 5 days.
Platelets have low levels of ABO antigens and can cause RhD sensitisation so need to know blood group.
Given to people with bone marrow failure, massive bleeding or DIC or low platelets and need surgery.
137
How are fractionated products (clotting factors, immunoglobulins, albumin etc) obtained?
Large pools.
| Some immunoglobulins rare - in too few people - so obtained via apheresis.
138
What is the "window period" of infections?
The time at the beginning of a new infection where a screening test will not show positive. It is therefore paramount that screening for blood donors doesn't rely only on these tests. Ask questions to exclude high risk donors and use voluntary, unpaid people.
