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TAS Haematology > Haemolysis ✅ > Flashcards

Haemolysis ✅ Flashcards

1
Q

What is haemolysis?

A

An increase in breakdown of RBCs

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2
Q

What happens if the bone marrow is unable to compensate for the increased red cell turnover in haemolysis?

A

Anaemia develops

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3
Q

What can haemolysis be broadly grouped into?

A
  • Inherited causes

- Acquired causes

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4
Q

What are inherited causes of haemolysis usually due to?

A

Intrinsic red blood cell abnormalities

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5
Q

What are acquired causes of haemolysis usually due to?

A

Extrinsic abnormalities

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6
Q

Give an example of an acquired mechanism of haemolysis?

A

Antibody-mediated destruction in immune haemolytic anaemias

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7
Q

What cause of haemolytic anaemias account for the majority of cases in children?

A

Intrinsic red cell abnormalities

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8
Q

What do blood tests show in haemolytic anaemia?

A
  • Reduced Hb
  • Raised reticulocytes
  • Raised unconjugated bilirubin
  • Raised LDH
  • Low haptoglobin
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9
Q

Why is LDH raised in haemolytic anaemia?

A

The LDH enzyme is present at high levels in RBCs, and so during haemolysis, lysis of RBCs causes large amounts of LDH to be released into the circulation

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10
Q

Where in the body does haemolysis occur?

A

Can occur in the circulation (intravascular) or in various organs, such as the spleen (extravascular)

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11
Q

What does intravascular haemolysis lead to?

A

Depletion of haptoglobin, increased LDH, and large numbers of fragmented red blood cells, called schistocytes.

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12
Q

Why does intravascular haemolysis lead to a depletion of haptoglobin?

A

Haptoglobin binds to free haemoglobin in the plasma to form a haptoglobin-haemoglobin complex, which is then removed from the circulation by the reticuloendothelial system (mostly in the spleen)

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13
Q

What happens after haptoglobin is depleted?

A

Free haemoglobin is filtered by the kidney

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14
Q

What happens to filtration of free haemoglobin by the kidney in severe cases of intravascular haemolysis?

A

The reabsorption is overwhelmed

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15
Q

Where in the body is LDH present?

A

It is present in many tissues, but has high concentrations within RBCs

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16
Q

Where does extravascular haemolysis take place?

A

Usually in spleen or liver, but can also occur in lung

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17
Q

What is the mechanism of extravascular haemolysis?

A

Spleen or liver macrophage Fc receptors bind immunoglobulin attached to red blood cells and then either ingest small portions of the cell membrane, creating spherocytes, or phagocytose the whole cells

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18
Q

What happens to the products of extravascular haemolysis?

A
  • Amino acids from globing chains are recycled
  • Iron is removed from haem and reused
  • Haem is degraded into unconjugated bilirubin
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19
Q

What provides useful clues into the diagnosis and aetiology of haemolysis?

A

The blood film

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20
Q

What might the blood film show in haemolysis?

A
  • Polychromasia
  • Sickle-shaped cells
  • Spherocytes
  • Fragmented red cells
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21
Q

What is polychromasia?

A

An increase in immature red blood cells (reticulocytes)

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22
Q

How do reticulocytes appear on most blood film stains?

A

Lilac

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23
Q

What is the significance of sickle-shaped cells in blood films?

A

Diagnostic of sickle cell disorders

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24
Q

When might spherocytes be seen on blood film?

A
  • Hereditary spherocytosis

- Immune haemolytic anaemias

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25
Q

What are the types of fragmented red blood cells?

A
  • Degmacytes, or ‘bite’ cells

- Schistocytes

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26
Q

What are bite cells typical of?

A

Oxidative haemolysis, e.g. G6PD deficiency

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27
Q

When are schistocytes seen?

A

In intravascular haemolysis, e.g. haemolytic uraemic syndrome

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28
Q

What does the direct antiglobulin test (DAT) detect?

A

The presence of antibodies coating RBCs

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29
Q

What is DAT essential for?

A

Diagnosis, or exclusion, of immune-mediated haemolytic anaemia

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30
Q

How is the DAT test performed?

A

RBCs are incubated with anti-human globulin (AHG), and if antibody is present on the cells, the AHG will cause agglutination

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31
Q

What is counted as a positive DAT?

A

If agglutination occurs

32
Q

Give 4 conditions where DAT is positive?

A
  • Haemolytic disease of the newborn
  • Autoimmune haemolytic anaemia
  • Drug-induced haemolytic anaemia
  • Haemolytic transfusion reactions
33
Q

What are the types of inherited haemolytic disorders?

A
  • Red cell membrane defects
  • Red cell enzyme defects
  • Haemoglobinopathies
34
Q

Give 2 red cell membrane defects

A
  • Hereditary spherocytosis

- Hereditary elliptocytosis

35
Q

Give 2 red cell enzyme defects

A
  • G6PD deficiency

- Pyruvate kinase deficiency

36
Q

Give 2 haemoglobinopathies

A
  • Sickle cell disorders, e.g. sickle cell anaemia

- Thalassaemias

37
Q

What are the types of acquired haemolytic disorders?

A
  • Autoimmune
  • Microangiopathic
  • Infection
  • Other
38
Q

Give 5 causes of autoimmune haemolytic anaemia?

A
  • Idiopathic
  • Rheumatological conditions
  • Infection-associated
  • Paroxysmal nocturnal haemoglobinuria
  • Lymphoproliferative disease
39
Q

Give 2 rheumatological conditions that can cause autoimmune haemolytic anaemia?

A
  • SLE

- JIA

40
Q

Give 2 infections that can cause autoimmune haemolytic anaemia?

A
  • Varicella zoster

- EBV

41
Q

Give a lymphoproliferative disease that can cause autoimmune haemolytic anaemia?

A

Hodgkin’s lymphoma

42
Q

Give 3 microangiopathic causes of haemolytic anaemia?

A
  • HUS
  • Thrombotic thrombocytopenia purpura
  • Haemangiomas
43
Q

Give an example of a haemangioma that can cause haemolytic anaemia?

A

Kasabach-Merritt syndrome

44
Q

Give 2 examples of infections that can cause haemolytic anaemia?

A
  • Malaria

- Sepsis

45
Q

Give 3 other causes of haemolytic anaemia

A
  • Hypersplenism
  • Burns
  • Poisoning
46
Q

Give 3 poisons that can cause haemolytic anaemia

A
  • Lead
  • Arsenic
  • Napthalene
47
Q

What is the most common inherited disorder of the red cell membrane?

A

Hereditary spherocytosis (HS)

48
Q

What are most cases of HS due to?

A

A mutation in spectrin or ankyrin genes

49
Q

What do spectrin and ankyrin genes do?

A

Encode key red cell membrane structural proteins

50
Q

What do the proteins encoded for my spectrin and ankyrin do?

A

Anchor the lipid membrane of the red cell to the protein skeleton

51
Q

What is the result of loss of the anchoring effect in HS?

A

Allows small membrane fragments to be lost during red cell passage through the spleen

52
Q

What happens as membrane loss progresses in HS?

A

The red cell gradually becomes spherical

53
Q

What happens to the spherocytic red cells in HS?

A

They are destroyed by the spleen, resulting in haemolytic anaemia

54
Q

What is the inheritance of HS?

A

Usually autosomal dominant, but up to 25% of cases are autosomal recessive, or the result of de novo mutations

55
Q

What are the clinical features of HS in most patients?

A
  • Mild anaemia (Hb 80-100)
  • Variable splenomegaly (typically 1-2 cm)
  • Fluctuating jaundice
56
Q

When in particular is there likely to be jaundice in mild HS?

A

At times of infection

57
Q

What can HS lead to in more severe cases?

A

Profound, chronic haemolytic anaemia

58
Q

When does HS usually present?

A

Early childhood or neonatal period

59
Q

Do neonates with HS require treatment?

A

Most will not, apart from phototherapy for jaundice

60
Q

What will around 25% of neonates with HS require?

A

1-3 transfusions due to moderately severe haemolytic anaemia during the first 1-2 months of life

61
Q

How common is transfusion dependence beyond neonatal life in HS?

A

Extremely uncommon

62
Q

How can a diagnosis of HS be made in most cases?

A

Positive family history and presence of spherocytes on the blood film

63
Q

What will blood tests show in HS?

A

Usually show mild anaemia with raised reticulocytes and bilirubin

64
Q

What is the most important differential for HS in neonates?

A

Haemolytic disease of the newborn

65
Q

How can HS be differentiated from haemolytic disease of the newborn?

A

In alloimmune haemolysis, DAT is almost always positive. In HS, it is negative

66
Q

What is usually enough for diagnosis of HS in those without family history?

A

Typical blood film findings and exclusion of other conditions

67
Q

What treatment is required for most patients with HS?

A

None, other than prophylactic oral folic acid to prevent megaloblastic anaemia

68
Q

What treatment can improve the anaemia in HS?

A

Splenectomy

69
Q

What is the problem with splenectomy in HS?

A

Side effects mean it is restricted to children who are failing to thrive or develop transfusion dependence

70
Q

What are the side effects of splenectomy?

A
  • Increased susceptibility to infection

- Risk of thrombosis

71
Q

What is common in older children and adults with HS?

A

Pigment gallstones due to chronic haemolysis

72
Q

What can complicate chronic haemolytic disorders?

A

Parvovirus B19 infection

73
Q

What can parvovirus B19 cause in chronic haemolytic disorders?

A

Severe reduction in red cell production (red cell aplasia)

74
Q

In what conditions can parvovirus B19 precipitate an aplastic crisis?

A

Any chronic haemolytic disorder

75
Q

What might support a diagnosis of parvovirus B19 as a cause of deterioration in children with chronic haemolytic disorders?

A

A preceding coryzal illness

76
Q

How can a diagnosis of aplastic crisis caused by parvovirus B19 be made in chronic haemolytic disorders?

A
  • Low Hb
  • Markedly reduced reticulocytes
  • IgM antibodies against parvovirus B19
77
Q

How low can the Hb be in aplastic crisis caused by parvovirus B19 infection?

A

Often 20-30g/L

TAS Haematology (7 decks)

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