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Haematology > The red blood cell and what can go wrong > Flashcards

The red blood cell and what can go wrong Flashcards

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1
Q

What do RBCs need to function?

A

efficient production (synthesis)
pliable (get through small vessels)
haemoglobin on which to carry oxygen
enzymes for metabolism
removal of defective cells

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2
Q

Define + describe erythropoiesis

A

RBC synthesis
in bone marrow
develop from common stem cell progenitor

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3
Q

What is the sequence from stem cell to mature RBC

A

stem cell –> erythroblast –> nucleated RBC –> reticulocyte –> mature RBCs

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4
Q

What are the requirements for erythropoiesis?

A

normal stem cell
normal maturation
healthy bone marrow microenvironment
growth factors (erythropoietin, GM-CSF)
essential components (iron, folate, vit B12, amino acids)

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5
Q

What is the shape of RBCs?

A

biconcave

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6
Q

Describe the structure of haemoglobin

A

tetramer –> 2 pairs globin chains (2 alpha, 2 beta)
haem molecule bound to each globin
iron within centre of haem

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7
Q

Describe haemoglobin production

A

3 phases = embryonic, foetal, adult
alpha chains:
- chromosome 16
- alpha in all Hb from foetal to adult

beta-like chains:
- beta in HbA adult
- gamma in HbF foetal
- delta in HbA2 in v low levels from week 30 gestation
- chromosome 11

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8
Q

What is the lifespan of a RBC and how are old RBCs removed?

A

120 days
old RBCs removed by macrophages –> found in spleen, liver and bone marrow

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9
Q

Define anaemia

A

reduced grams of Hb/L blood
below the age/sex adjusted normal range

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10
Q

What can cause anaemia?

A

too few RBCs
too little haemoglobin
an abnormally low haematocrit

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11
Q

Define haematocrit

A

ratio RBC:plasma
reduced if decreased RBCs or increased plasma

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12
Q

Anaemia symptoms

A

acute onset = symptoms more marked
chronic onset = less severe symptoms, time for body to compensate
fatigue + weakness
dyspnoea (breathlessness)
tachycardia (palpitations)
muscle cramps
angina/heart failure

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13
Q

Anaemia signs

A

pallor
tachypnoea
tachycardia
hypotension

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14
Q

What is MCV?

A

mean corpuscular volume
low MCV = microcytic
normal MCV = normocytic
high MCV = macrocytic

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15
Q

List causes of microcytic anaemia

A

iron deficiency
thalassaemia
anaemia of chronic disease
lead poisoning (rare)
sideroblastic anaemia (rare)

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16
Q

List causes of normocytic anaemia

A

anaemia of chronic disease
acute blood loss
chronic renal failure
mixed B12/folate + iron deficiency
bone marrow disorders

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17
Q

List causes of macrocytic anaemia

A

B12 or folate deficiency
liver disease
drugs (including alcohol)
reticulocytosis (haemolysis)
hypothyroidism
myelodysplasia
pregnancy

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18
Q

How else (other than MCV) can anaemia be classified?

A

decreased RBC production or increased RBC destruction or loss

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19
Q

Reduced red cell production causes

A

defective stem cells
defective maturation
unhealthy microenvironment
absence of stimulation by growth factors
lack of components for RBC formation

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20
Q

Reduced RBC production lab findings

A

usually normocytic and normochromic (unless deficiency B12, iron or folate)
reticulocytes not raised

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21
Q

Describe anaemia of chronic disease

A

ineffective iron utilisation due to raised hepcidin
mild to moderate (rarely <90g/L)
normochromic + normocytic (sometimes microcytic)
chronic inflammation (eg. RA, IBD)
chronic infection (eg. pneumonia, TB)
malignant disease

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22
Q

Define haemolysis

A

premature breakdown of RBCs (<120 days)
increased RBC destruction

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23
Q

Haemolysis signs

A

jaundice
dark urine
gallstones (RBC pigment)

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24
Q

Haemolysis blood results

A

anaemia (normocytic or macrocytic (reticulocytosis))
increased reticulocyte count
increased bilirubin
increased LDH
decreased haptoglobin

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25
What are the 2 overarching causes of haemolysis?
intrinsic (abnormality within cell) extrinsic (abnormality outside cell)
26
3 intrinsic haemolysis causes
membrane metabolism (enzymes) haemoglobin
27
Describe membrane abnormalities that cause haemolysis
Inherited: - hereditary spherocytosis - hereditary elliptocytosis - hereditary stomatocytosis consequences = RBC more easily damaged, macrophage removal, shortened RBC life autosomal dominant cause of prolonged neonatal jaundice mild anaemia fluctuant jaundice gallstones aplastic crises precipitated by Parvovirus (B19)
28
RBC membrane defects lab findings
anaemia (usually mild) reticulocytosis increased bilirubin increased LDH blood film = abnormally shaped RBC direct antibody test negative
29
RBC membrane defects treatment
folic acid splenectomy
30
Describe enzyme defects that cause haemolysis
inherited G6PD deficiency = most common inability of RBC to protect itself from oxidative stress by glutathione production X-linked recessive African/Mediterranean descent > acute episodes of haemolysis following oxidative stress (eg. drugs, infections, moth balls, Fava beans)
31
Define haemoglobinopathy
disorder of haemoglobin synthesis
32
Describe haemoglobin production
alpha globin chains made from foetus onwards - 4 genes, 2 each chromosome pair with beta-like globin chains - 2 genes, 1 each chromosome gamma (alpha 2, gamma 2) in foetus decline at birth, very low by 6 mo, HbF beta (alpha 2, beta 2) from roughly 30 weeks gestation, HbA delta (alpha 2, delta 2) very low levels from 30 weeks, HbA2
33
Describe thalassaemia
reduced globin chain synthesis common in Asia, Africa + south Mediterranean reduced/no alpha/beta chains produced
34
Consequences of thalassaemia
chain imbalance excess alpha/beta chains precipitate precipitated chains damage RBC membrane damaged cells destroyed prematurely by macrophages
35
Describe thalassaemia classification
alpha thalassaemia = too few alpha chains beta thalassaemia = too few beta chains thalassaemia major = no alpha/beta chains thalassaemia trait = reduced alpha/beta chains, no transfusions required thalassaemia intermedia = intermediate clinical picture
36
Describe the clinical aspect of beta thalassaemia major
severe anaemia from 3-6 mo hepatosplenomegaly expansion of bone marrow detected by newborn screening programme
37
Describe the clinical aspect of alpha thalassaemia major
fatal in utero (hydrops fetalis) often alpha gene deletions HbH disease = born with 1/4 alpha genes variable phenotype
38
Describe the clinical aspect of thalassaemia trait
1 beta gene normal mild microcytic anaemia 'carrier' can pass gene to child asymptomatic 2 x beta thalassaemia trait procreate = 1/4 chance offspring will have beta thalassaemia major increased % Hb = HbA2 (2 alpha, 2 delta)
39
What is Alpha-0 thalassaemia?
2 genes deleted from same chromosome risk of alpha thalassaemia major in offspring
40
What is Alpha+ thalassaemia?
2 genes deleted from different chromosomes risk of alpha thalassaemia major in offspring not present
41
How is thalassaemia/thalassaemia trait diagnosed?
hypochromic microcytic anaemia (exclude Fe deficiency) Hb electrophoresis or HPLC (high performance liquid chromatography) - beta thalassaemia trait = increased HbA2 - beta thalassaemia major = absence HbA - cannot pick up alpha trait genetic analysis required for alpha thalassaemia diagnosis
42
Thalassaemia management
major: - lifelong transfusions (keep Hb >100g/L) [iron overload = iron chelators remove iron excess) - splenectomy (reduce blood requirements) - allogenic bone marrow transplant (success >80%) trait: - avoid iron unless Fe deficient - genetic counselling
43
Describe sickle cell anaemia
abnormal globin chain structure point mutation leads to single amino acid substitution (valine --> glutamate at position 6beta chain --> forms HbS) HbS forms crystals when exposed to low oxygen levels --> causes 'sickling' of RBCs homozygous = disease heterozygous = trait
44
Sickle cell anaemia presentation
chronic haemolytic anaemia from 3-6mo (when HbF-->HbA) rate of haemolysis may increase during crisis Hb~60-90g/L (anaemia symptoms mild) elongated red cells with pointy ends
45
Describe sickle cell trait
1 gene affected benign condition no/mild anaemia normal RBC appearance HbS = 25-45% total Hb care taken during anaesthesia + high altitudes --> extreme low oxygen can cause sickling genetic counselling
46
Describe blood vessel occlusion in sickle cell disease
sickle cells can cause tissue infarction by blocking blood vessels due to shape + 'stickiness'
47
Sickle cell disease complications
occlude vessels: - pain (especially bones) - organ damage - splenic infarction from age 2 (autosplenectomy) - organ engorgement with blood (sequestration --> spleen, liver)
48
Sickle cell disease lab findings
blood film: - sickle cells - target cells - nucleated red cells - Howell-Jolly bodies (splenic atrophy) sickle solubility screen positive (HbS less soluble when oxygen levels low) Hb electrophoresis/HPLC shows HbS, no HbA, variable amounts HbF)
49
Sickle cell management
prophylactic: - avoid precipitating factors - folic acid - pneumococcal vaccine, regular oral penicillin - hydroxycarbamide crises: - analgesia (opiates) - rest - rehydration - oxygen +/- antibiotics - blood transfusion/exchange transfusion (severe/chest crises) stem cell transplantation
50
List 4 extrinsic causes of haemolysis
antibody attack mechanical trauma infections chemical + physical agents
51
Describe how antibody attack causes haemolysis
antibodies primed to only attack foreign cells autoimmunity = antibodies attack own cells antibodies attacking RBC = autoimmune haemolytic anaemia (AIHA)
52
Describe how antibody attack causes haemolysis
antibodies primed to only attack foreign cells autoimmunity = antibodies attack own cells antibodies attacking RBC = autoimmune haemolytic anaemia (AIHA)SE
53
Describe autoimmune haemolytic anaemia (AIHA) testing
direct antiglobulin test (Coombs) anti-human Ig added, if antibody on red cells, agglutination will occur due to crosslinking warm = antibody reacts with RBC at 37 degrees celsius (IgG) cold = antibody reacts with RBC < 37 degrees celsius (IgM)
54
Describe warm AIHA
antibody reacts with RBC at 37 degrees celsius (IgG) idiopathic or secondary to: - autoimmune conditions - disordered immune system (CLL, low grade lymphoma) - drugs (RBC membrane complex --> penicillin)(Ab against RBC membrane --> methyldopa)
55
Describe cold AIHA
antibody reacts with RBC < 37 degrees celsius (IgM) idiopathic or secondary to: - lymphoma - infections (mycoplasma pneumonia, EBV) - paroxysmal cold haemoglobinuria (rare, syphilis)
56
AIHA lab findings
Haemolysis: - anaemia - reticulocytosis - increased LDH - increased unconjugated bilirubin +ve DAT (Coombs) blood film = spherocytes (IgG), agglutination (IgM)
57
AIHA management
remove/treat underlying cause keep patient warm if IgM (cold-reacting) folic acid transfusion immune suppression (warm = corticosteroids, cold+warm = rituximab) splenectomy for resistant cases (less helpful if IgM)
58
What infection can cause haemolysis?
malaria
59
Name 5 microangiopathic haemolytic anaemia causes?
DIC (disseminated intravascular coagulation) TTP (thrombotic thrombocytopenic purpura) HUS = haemolytic uremic syndrome faulty mechanical heart valves march haemoglobinuria
60
What chemicals/physical agents can cause haemolysis?
drugs (dapsone) copper (wilson's disease) lead burns snake + spider bites
61
What is PNH?
paroxysmal nocturnal haemoglobinuria - small print cause of intravascular haemolysis - rare - acquired defect marrow stem cells - defect in anchorage of surface proteins because of absence of glycosyl phosphatidyllinositol (GP) - RBC rendered sensitive to lysis by complement
62
Define haemoglobinopathy
An inherited condition in which haemoglobin does not function properly as there are mutations in haemoglobin

Haematology (16 decks)

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