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Haematology > Haemolysis > Flashcards

Haemolysis Flashcards

1
Q

What is haemolysis?

A

Haemolysis is the premature destruction of erythrocytes

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2
Q

Why are erythrocytes susceptible to haemolytic damage?

A
  • They have a biconcave shape
  • They have limited metabolic reserve and rely only on glycolysis for energy
  • They can’t generate new proteins once in the circulation
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3
Q

What are the 2 main stages of haemolysis

A
  • Compensated haeolysis
  • Haemolytic anaemia (Decompensated)
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4
Q

What is meant by compensated haemolysis?

A

Compensated haemolysis is increased red cell destruction, compensated by increased red cell production, so Hb concentration is maintained

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5
Q

What are the 2 ways in which haemolysis can be classified?

A

By site of haemolysis
By pathophysiology

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6
Q

What are the 2 classifications of haemolysis based on site?

A

Extravascular
Intravascular

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7
Q

What are the 4 classifications of haemolysis based on pathophysiology?

A
  • Premature destruction by extrinsic mechanism
  • Abnormality of cell membrane
  • Abnormality of red cell metabolism
  • Abnormality of haemoglobin structure
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8
Q

What are some possible consequences of haemolysis?

A
  • Erythroid hyperplasia
  • Reticulocytosis
  • Excess RBC breakdown products (e.g. bilirubin)
  • Clinical features that differ by aetiology and site of breakdown
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9
Q

How will bone marrow respond to haemolysis?

A

Reticulocytosis and erythroid hyperplasia, meaning the store of precursor cells undergoes hyperplasia to produce more red blood cells (Erythroid hyperplasia) and in turn generates more reticulocytes (Reticulocytosis)

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10
Q

How can reticulocytosis be measured?

A

Automated reticulocyte counting can be used in which ribosomal RNA is labelled with fluorochrome and the fluorescent cells are counted

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11
Q

What investigations are may be required in haemolysis?

A
  • FBC + blood film to identify causes
  • Serum unconjugated bilirubin raised
  • Serum haptoglobins low (As bind free Hb so will be consumed in haemolysis)
  • Urinary urobilinogen raised
  • Lactate dehydrogenase (LDH) raised - Non-specific
  • History and examination - Family history, organomegaly
  • Direct Coomb’s test
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12
Q

How will blood film show membrane damage?

A

Spherocytes

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13
Q

How will blood film show mechanical damage?

A

Red cell fragments

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14
Q

How will blood film show oxidative damage?

A

Heinz bodies

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15
Q

What are Heinz bodies?

A

These are condensed precipitates of oxidised globulins

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16
Q

What are spherocytes?

A

These are spherical, small red blood cells

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17
Q

How do spherocytes form?

A

Red cells have an excess of membrane to give it a large SA:V ratio

If the membrane is removed to the point where it is the least amount of membrane required to enclose the Hb, then it forms a sphere

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18
Q

What are some causes of spherocytosis?

A
  • Hereditary spherocytosis
  • Warm (IgG) haemolytic anaemia
  • Delayed transfusion reaction
  • Haemolytic disease of the newborn
  • Zieve’s syndrome
  • Drug induced haemolysis
  • Fresh-water drowning (Cells swell due to increased water)
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19
Q

What is extravascular haemolysis?

A

Increased destruction of red blood cells by the reticuloendothelial system (Spleen and liver macrophages)

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20
Q

Describe the pathophysiology of extravascular haemolysis

A

Normally, old erythrocytes are taken up with the reticuloendothelial system (Spleen and liver) and engulfed by macrophages

In cases of hyperplasia at destruction sites such as splenomegaly or hepatomegaly, there will excess normal destruction erythrocytes

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21
Q

What are some clinical presentations of extravascular haemolysis?

A

Jaundice
Gall stone formation
Dark urine
Symptoms of anaemia

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22
Q

How can extravascular haemolysis cause jaundice, gallstones and dark urine?

A

Increased extravascular haemolysis will cause the release of protoporphyrin, leading to increased production of unconjugated bilirubin and urobilinogen

Unconjugated bilirubinaemia will lead to jaundice and possible gall stone formation (Chronic)

Urobilinogenuria will lead to dark urine production

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23
Q

What is intravascular haemolysis?

A

This is haemolysis that occurs within circulation, leading to the release of erythrocyte contents into the blood

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24
Q

What are some haematological changes that will occur in intrinsic haemolysis?

A
  • Haemoglobinaemia - Free Hb in circulation
  • Methaemalbuminaemia - Hb mopped up by albumin
  • Haemoglobinuria
  • Haemosiderinuria - Iron taken up by tubular cells and converted to haemosiderin, the cells are later shed into the urine
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25
Q

How will haemoglobinuria present?

A

Excretion of pink urine which turns black on standing

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26
Q

What are some causes of intravascular haemolysis?

A
  • ABO incompatible blood transfusion
  • Severe G6PD deficiency
  • Severe falciparum malaria (Blackwater fever)
  • Paroxysmal nocturnal hemoglobinuria (Premature WBC breakdown)
  • Paroxysmal cold hemoglobinuria (Immune RBC breakdown)
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27
Q

Why is blackwater fever named as such?

A

Blackwater fever is named for the black urine on standing caused by haemoglobinuria

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28
Q

What is meant by “premature destruction of normal erythrocytes”?

A

This is the early destruction of red blood cells, despite there being no physical abnoralities of the red blood cells

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29
Q

What are the 2 mechanisms of premature destruction of normal erythrocytes?

A

Immune mechanisms
Mechanical mechanisms

30
Q

What are the 2 main immune mechanisms of premature destruction of erythrocytes?

A
  • Autoimmune haemolysis
  • Alloimmune haemolysis
31
Q

What is meant by autoimmune haemolysis?

A

Autoimmune haemolysis is caused by autoantibodies that bind to self-proteins on red cells

32
Q

What are the 2 types of antibodies present in autoimmune haemolysis?

A

IgG (Warm autoimmune haemolysis)
IgM (Cold autoimmune haemolysis)

33
Q

What are some causes of warm (IgG) autoimmune haemolysis?

A
  • Idiopathic
  • Autoimmune disorders (E.g. SLE)
  • Lymphoproliferative disorders (E.g. CLL)
  • Drugs (E.g. penicillins)
  • Infections
34
Q

What are some causes of cold (IgM) autoimmune haemolysis?

A
  • Idiopathic
  • Infections (EBV, mycoplasma)
  • Lymphoproliferative disorders
35
Q

What test is required to test for autoimmune haemolysis?

A

Direct Coomb’s (Anti-globulin) test

36
Q

How does a direct Coomb’s test work?

A

This involves Coomb’s reagent, which is a monocloncal antibody against autoantibodies on red blood cells, which will cause agglutination in positive patients

37
Q

What is alloimmune haemolysis?

A

This is a condition in which someone elses antibodies attack your cells, or your antibodies attack someone elses cells

38
Q

What is the most common cause of alloimmune haemolysis?

A

ABO mismatched transfusions

39
Q

What types of alloimmune reactions will lead to intravascular, rapid haemolysis?

A

If the IgM antibodies of the patient attack the donated blood cells, or the donated antibodies attack the A/B antigens

40
Q

What types of alloimmune reactions will lead to extravascular, slow haemolysis?

A

If the IgG antibodies of the patient attack te donated blood cells, or the donated antibodies attack the rhesus proteins,

41
Q

What is haemolytic disease of the newborn?

A

Haemolytic disease of the newborn occurs when the mum’s IgG antibodies attacks the baby’s cells (RhD or ABO incompatability)

42
Q

What is haemolytic disease of the newborn?

A

This is immune-mediated disease caused by destruction of red blood cells in the foetus, by antibodies produced by the mother

43
Q

Describe the pathophysiology of haemolytic disease of the newborn

A
  1. During birth, Rh+ foetal erythrocytes leak into maternal blood after breakage of the embryonic chorion which isolates the two types of blood
  2. Maternal B cells are activated by Rh antigens and produce IgG
    • IgG binds to D-antigens on erythrocytes
  4. IgG can activate the complement system , converting C3 into C3b, which binds to the cells and allows for the conversion of C5 to C5b, which allows for the formation of the membrane attack complex (MAC)
  5. This causes osmotic lysis of the erythrocytes, causing the release of free haemoglobin which is broken down into unconjugated bilirubin
44
Q

Why will only IgG cause haemolytic disease of the newborn, and not IgM?

A

IgM cannot cross the placental wall, whereas IgG can

45
Q

What is meant by an indirect Coomb’s test?

A

This is when blood is taken and tested using Coomb’s reagent from the mother, not the child itself

46
Q

How is haemolytic disease of the newborn managed?

A

Phototherapy
IV immunoglobulin
Exchange transfusion

47
Q

How does phototherapy work in haemolytic disease of the newborn?

A

Energy within light is enough to convert unconjuagated bilirubin into water-soluble, photoisomers of bilirubin

48
Q

What type of light is used in phototherapy for haemolytic disease of the newborn?

A

Blue light (No UV)

49
Q

What are the uses of IV immunoglobulins in heamolytic disease of the newborn?

A

This is used to prevent further phagocytosis and haemolysis in haemolytic jaundice

50
Q

What is a risk of IV immunoglobulin in haemolytic disease of the newborn?

A

Can cause circulatory instability

51
Q

What is an exchange transfusion?

A

This is an intensive and invasive procedure in which a certain volume of blood is pumped out of the body, while the same volume is transfused in to clean unconjugated blood out of the system

52
Q

What are some causes of unconjugated hyperbilirubinaemia in neonates?

A

Physiological
Breast milk jaundice
Haemolytic disease of the newborn
Inherited disorders of bilirubin metabolism

53
Q

What are some examples of inherited disorders of bilirubin metabolism?

A
  • Gilbert’s syndrome
  • Crigler-Najjar syndrome
  • Rotor syndrome
  • Dubin-Johnson syndrome
54
Q

What is meant by physiological jaundice in newborns?

A

Liver immaturity leads to an increased turnover of red blood cells, leading to increased bilirubin levels

55
Q

How can breast milk cause jaundice?

A

There is a possible inhibitor of bilirubin conjugation found in breast milk

56
Q

What are some mechanical mechanisms of premature destruction of erythrocytes?

A
  • Disseminated intravascular coagulation
  • Haemolytic uraemic syndrome (E.g. E.coli 0157)
  • Thrombotic thrombocytopenic purpura
  • Severe burns
  • Damaged heart valves
  • Rupture of infected red cells by malaria parasites
57
Q

How does haemolytic uremic syndrome occur?

A

Infection, such as from E.coli 0157, leads to renal failure, which leads to damage to blood vessels and thus damage to red blood cells

58
Q

How do severe burns cause premature destruction of normal erythrocytes?

A

In severe burns, damaged capillaries shear off the membrane of red cells, leading to formation of microspherocytes

59
Q

What are some causes of acquired abnormal cell membranes in haemolysis?

A
  • Zeive’s syndrome
  • Paroxysmal nocturnal haemoglobinuria
60
Q

What is Zieve’s syndrome?

A

This is caused by build up of cholesterol in the liver vessels, causing damage to red blood cells

61
Q

What are some congenital causes of cell membrane abnormalities in haemolysis?

A
  • Reduced membrane deformibility
  • Increased transit time through spleen
  • Oxidant envirnonment in spleen
  • Hereditary spherocytosis
62
Q

How are erythrocyte cell membrane abnormalities usually managed?

A
  • Folic acid supplementation
  • Possible transfusion (Especially in infection, most commonly parvovirus)
  • Splenectomy (Spleen removes membranes, so splenectomy extends red cell survival)
63
Q

What are some possible consequences of splenectomy?

A

Increased risk of pneumonia, meningitis and other encapsulated bacterias

64
Q

What are some causes of abnormal erythrocyte metabolism?

A
  • G6PD deficiency
  • Dapsone or salazopyrin can increase oxidative stress
  • Onions and garlic cause oxidative stress in dogs
65
Q

What is G6PD deficiency?

A

G6PD deficiency is an X-linked condition resulting in hundreds of mutations , which can cause oxidative stress

66
Q

How will mild G6PD deficiency present?

A

Mild G6PD only causes effects with other oxidative stress (e.g. infection, drugs, fava beans, chainti)

67
Q

What are some causes of oxidative stress to erythrocytes?

A
  • Infection
  • Drugs (e.g. dapsone)
  • Fava beans
  • Chianti
68
Q

How will severe G6PD deficiency present?

A

Severe G6PD will lead to background chronic haemolysis, which is then exacerbated by the above

69
Q

How does dapsone (and onions and garlic in dogs) affect red cells?

A

These will lead to formation of heinz bodies and keratocytes

Cells containing these will have them removed by macrophages, leaving a horn shaped membrane

These horned cells are known as keratocytes (Kerat = Horn)

70
Q

What is the main cause of abnormal haemoglobin structure, leading to haemolysis?

A

Sickle cell diseases

71
Q
A

Haematology (32 decks)

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