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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

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
Q

What are the 2 overarching causes of haemolysis?

A

intrinsic (abnormality within cell)
extrinsic (abnormality outside cell)

26
Q

3 intrinsic haemolysis causes

A

membrane
metabolism (enzymes)
haemoglobin

27
Q

Describe membrane abnormalities that cause haemolysis

A

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
Q

RBC membrane defects lab findings

A

anaemia (usually mild)
reticulocytosis
increased bilirubin
increased LDH
blood film = abnormally shaped RBC
direct antibody test negative

29
Q

RBC membrane defects treatment

A

folic acid
splenectomy

30
Q

Describe enzyme defects that cause haemolysis

A

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
Q

Define haemoglobinopathy

A

disorder of haemoglobin synthesis

32
Q

Describe haemoglobin production

A

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
Q

Describe thalassaemia

A

reduced globin chain synthesis
common in Asia, Africa + south Mediterranean
reduced/no alpha/beta chains produced

34
Q

Consequences of thalassaemia

A

chain imbalance
excess alpha/beta chains precipitate
precipitated chains damage RBC membrane
damaged cells destroyed prematurely by macrophages

35
Q

Describe thalassaemia classification

A

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
Q

Describe the clinical aspect of beta thalassaemia major

A

severe anaemia from 3-6 mo
hepatosplenomegaly
expansion of bone marrow
detected by newborn screening programme

37
Q

Describe the clinical aspect of alpha thalassaemia major

A

fatal in utero (hydrops fetalis)
often alpha gene deletions
HbH disease = born with 1/4 alpha genes
variable phenotype

38
Q

Describe the clinical aspect of thalassaemia trait

A

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
Q

What is Alpha-0 thalassaemia?

A

2 genes deleted from same chromosome
risk of alpha thalassaemia major in offspring

40
Q

What is Alpha+ thalassaemia?

A

2 genes deleted from different chromosomes
risk of alpha thalassaemia major in offspring not present

41
Q

How is thalassaemia/thalassaemia trait diagnosed?

A

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
Q

Thalassaemia management

A

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
Q

Describe sickle cell anaemia

A

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
Q

Sickle cell anaemia presentation

A

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
Q

Describe sickle cell trait

A

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
Q

Describe blood vessel occlusion in sickle cell disease

A

sickle cells can cause tissue infarction by blocking blood vessels due to shape + ‘stickiness’

47
Q

Sickle cell disease complications

A

occlude vessels:
- pain (especially bones)
- organ damage
- splenic infarction from age 2 (autosplenectomy)
- organ engorgement with blood (sequestration –> spleen, liver)

48
Q

Sickle cell disease lab findings

A

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
Q

Sickle cell management

A

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
Q

List 4 extrinsic causes of haemolysis

A

antibody attack
mechanical trauma
infections
chemical + physical agents

51
Q

Describe how antibody attack causes haemolysis

A

antibodies primed to only attack foreign cells
autoimmunity = antibodies attack own cells
antibodies attacking RBC = autoimmune haemolytic anaemia (AIHA)

52
Q

Describe how antibody attack causes haemolysis

A

antibodies primed to only attack foreign cells
autoimmunity = antibodies attack own cells
antibodies attacking RBC = autoimmune haemolytic anaemia (AIHA)SE

53
Q

Describe autoimmune haemolytic anaemia (AIHA) testing

A

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
Q

Describe warm AIHA

A

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
Q

Describe cold AIHA

A

antibody reacts with RBC < 37 degrees celsius (IgM)

idiopathic or secondary to:
- lymphoma
- infections (mycoplasma pneumonia, EBV)
- paroxysmal cold haemoglobinuria (rare, syphilis)

56
Q

AIHA lab findings

A

Haemolysis:
- anaemia
- reticulocytosis
- increased LDH
- increased unconjugated bilirubin

+ve DAT (Coombs)
blood film = spherocytes (IgG), agglutination (IgM)

57
Q

AIHA management

A

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
Q

What infection can cause haemolysis?

A

malaria

59
Q

Name 5 microangiopathic haemolytic anaemia causes?

A

DIC (disseminated intravascular coagulation)
TTP (thrombotic thrombocytopenic purpura)
HUS = haemolytic uremic syndrome
faulty mechanical heart valves
march haemoglobinuria

60
Q

What chemicals/physical agents can cause haemolysis?

A

drugs (dapsone)
copper (wilson’s disease)
lead
burns
snake + spider bites

61
Q

What is PNH?

A

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
Q

Define haemoglobinopathy

A

An inherited condition in which haemoglobin does not function properly as there are mutations in haemoglobin

Haematology (16 decks)

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