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Haematology > Haemolysis > Flashcards

Haemolysis Flashcards

1
Q

what is haemolysis?

A

premature red cell destruction (shortened RBC survival)

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2
Q

why are red cells particularly susceptible to damage?

A

they need to have a biconcave shape to transit the circulation successfully
they have limited metabolic reserve and rely exclusively on glucose metabolism for energy (no mitochondria)
cant generate new proteins once in the circulation (no nucleus)

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3
Q

what is compensated haemolysis?

A

increased red cell destruction compensated by increased red cell production
i.e - Hb concentration is maintained

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4
Q

what is haemolytic anaemia?

A

decompensated haemolysis
increased rate of red cell destruction exceeding bone marrow capacity for red cell production
i.e - Hb concentration falls

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5
Q

2 main consequences of haemlysis?

A 
erythroid hyperplasia (increased bone marrow red cell production)
excess red cell breakdown products e.g bilirubin
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6
Q

how can red cell survival be measured?

A

not possible to directly measure
rely on detecting the consequences of haemolysis and then investigating the cause
- increased RBC production (look for signs of erythroid hyperplasia in blood)
- detection of breakdown products

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7
Q

2 responses to haemolysis in bone marrow?

A

reticulocytosis

erythroid hyperplasia

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8
Q

what are reticulocytes?

A

non-nucleated precursors of erythrocytes
don’t have the central pallor that mature RBCs have
not diagnostic of haemolysis, occur in response to bleeding, iron therapy in iron deficiency anaemia

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9
Q

how is reticulocytosis measured?

A

automated reticulocyte counting

ribosomal RNA is labelled with a fluorochrome and fluorescent cells are counted

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10
Q

how can haemolysis be classified?

A

extravascular vs intravascular

different mechanisms and breakdown products

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11
Q

extravascular haemolysis?

A

RBCs taken up by reticuloendothelial system (spleen and liver predominantly)

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12
Q

intravascular haemolysis?

A

RBCs destroyed within circulation

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13
Q

which classification of haemolysis is more common?

A

extravascular

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14
Q

features of extravascular haemolysis?

A

hyperplasia at site of destruction (splenomegaly +/- hepatomegaly)
release of protoporphyrin causing unconjugated bilirubinaemia (results in jaundice and gall stones) and urobilinogenuria
normal products but in excess

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15
Q

features of intravascular haemolysis?

A

RBCs destroyed within circulation and contents spilled out causing:
- haemoglobinaemia (free Hb in circulation)
- methaemalbuminaemia
haemoglobinuria (pink urine, turns black on standing)
- haemosiderinuria
abnormal poducts

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16
Q

which classification of haemolysis can be life threatening?

A

intravascular

17
Q

causes of intravascular haemolysis?

A

ABO incompatible blood transfusion
G6PD deficiency
severe falciparum malaria (blackwater fever)
PNH,PCH (rare)

18
Q

causes of extravascular haemolysis?

A

basically every other cause of haemolysis

19
Q

investigations in haemolysis to confirm haemolytic state?

A 
FBC + blood film
reticulocyte count
serum unconjugated bilirubin
serum haptoglobins
urinary urobilinogen
20
Q

investigations to identify cause of haemolysis?

A

history and examination (shows whether genetic/acquired)
blood film
specialist investigations (coombs test etc)

21
Q

what might be found on blood film?

A 
membrane damage (spherocytes)
mechanical damage (red cell fragments)
oxidative damage (Heinz bodies)
others (e.g HbS - sickle cells)
22
Q

how else can haemolysis be classified?

A 
by site of defect
- premature destruction of normal RBCs (immune/mechanical)
- abnormal cell membrane
- abnormal RBC metabolism
- abnormal Hb
(all can be congenital or acquired)
23
Q

causes of acquired immune haemolysis?

A

autoimmune haemolysis

alloimmune haemolysis

24
Q

causes of autoimmune haemolysis?

A

warm or cold autoantibody

  • warm (IgG) = most common
  • cold (IgM) = less common
25
Q

what is warm IgG autoantibody autoimmune haemolysis associated with?

A 
idiopathic (most common)
autoimmune disorders (SLE etc)
lymphoproliferative disorders (CLL)
drugs (penicillins etc)
infections (cross reactive antibodies etc)
26
Q

what is cold (IgM) autoantibody autoimmune haemolysis associated with?

A

idiopathic
infections (EBV, mycoplasma)
lymphoproliferative disorders

27
Q

what does direct coombs test do?

A 
identifies antibody (and complement) bound to own red cells
identifies agglutination when antibodies and RBCs react
28
Q

causes of alloimmune haemolysis?

A 
immune response (antibody produced) - e.g haemolytic transfusion reaction
passive transfer of antibody - e.g haemolytic disease of newborn
29
Q

how does haemolytic transfusion reaction cause alloimmune haemolysis?

A

immediate (IgM) predominantly causes intravascular haemolysis
delayed (IgG) predominantly causes extravascular haemolysis

30
Q

causes of acquired mechanical haemolysis?

A 
disseminated intravascular coagulation
haemolytic uraemic syndrome (e.g E.coli 0157)
TTP
leaking heart valve
infections (e.g malaria)
31
Q

acquired causes of haemolysis due to abnormal cell membrane?

A 
liver disease (sieve's syndrome)
vitamin E deficiency
paroxysmal nocturnal haemoglobinuria
32
Q

what is sieve’s syndrome?

A

haemolysis
alcoholic liver disease
hyperlipidaemia
causes anaemia, polychromatic macrocytes and irregularly contracted cells)

33
Q

congenital causes of haemolysis due to abnormal RBC membrane?

A

reduced membrane deformability
increased transit time through spleen
oxidant environment in spleen causes extravascular RBC destruction
hereditary spherocytosis

34
Q

congenital causes of haemolysis due to abnormal RBC metabolism?

A

disturbance in enzyme pathways

e.g G6PD deficiency due to failure to cope with oxidative stress > failure to generate ATP > metabolic processes fail

35
Q

what can cause significant stress in metabolic pathways of normal cells enough to cause oxidative damage?

A

dapsone

salazopyrin

36
Q

congenital causes of haemolysis due to abnormal haemoglobin?

A

sickle cell disease (presence of haemoglobin S)

37
Q

what happens in sickle cell disease?

A

point mutation in beta globin chain

HbS affects physical properties of Hb (abnormal polymerisation) resulting in shortened RBC survival

Haematology (26 decks)

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