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Haematology > Haemoglobinopathies > Flashcards

Haemoglobinopathies Flashcards

1
Q

Which type of haemoglobin is predominant in adults and what are its components?

A

HbA –> 2 alpha + 2 beta chains

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2
Q

What is HbA2 composed of?

A

2 alpha + 2 delta chains

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3
Q

What is HbF and what is it composed of?

A

Foetal Hb –> 2 alpha + 2 gamma chains

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4
Q

When will a child usually reach adult levels of HbA?

A

Age 6-12 months (so beta chain problems wont manifest until then)

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5
Q

What are haemoglobinopathies?

A

Hereditary, autosomal recessive conditions

Affecting globin chain synthesis

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6
Q

What are the two main groups of haemoglobinopathies?

A

Thalassaemias (decreased rate of globin synthesis)

Structural Hb variants (normal production of abnormal globin chain e.g. HbS)

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7
Q

What are the two main types of thalassaemia?

A

Alpha thalassaemia

Beta thalassaemia

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8
Q

Describe the different severities of alpha thalassaemia

A

Alpha chain has 2 genes, so 4 alleles:

  • 1 allele affected = silent carrier
  • 2 alleles affected = trait
  • 3 alleles affected = HbH disease
  • 4 alleles affected = Hb Barts
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9
Q

Describe the different severities of beta thalassaemia

A

Beta chain has 1 gene, so 2 alleles:

  • 1 allele affected = trait
  • 2 partially functioning alleles = thalassaemia intermedia
  • 2 non-functioning alleles = thalassaemia major
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10
Q

What are the features of Hb Bart?

A

Causes intrauterine haemolytic anaemia + hydrops fetalis –> usually fatal

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11
Q

In which geographical areas is alpha thalassaemia most common?

A

SE Asia
Africa
India

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12
Q

In which geographical areas in beta thalassaemia most common?

A

Mediterranean
Middle East
Central/South Asia
China

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13
Q

Which signs/symptoms are seen in both alpha and beta thalassaemia?

A

Haemolytic anaemia:

  • SOB
  • fatigue
  • pallor
  • murmur from increased CO
  • splenomegaly +/- hepatomegaly
  • failure to thrive, reduced growth
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14
Q

Which additional features might be seen in beta thalassaemia?

A 
Jaundice
Facial dysmorphia:
- frontal bossing
- maxillary hypertrophy
- large head
Osteopenia
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15
Q

Which sign might be the only feature in thalassaemia trait/minor?

A

Microcytic anaemia

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16
Q

How is thalassaemia diagnosed?

A

Hb electrophoresis or chromatography

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17
Q

Which electrophoresis finding is characteristic of beta thalassaemia trait?

A

Increased HbA2

18
Q

What would be seen on electrophoresis in beta thalassaemia major?

A

Mainly HbF, no HbA

19
Q

What would be seen on electrophoresis in HbH disease?

A

HbH –> excess beta chains form B4 tetramers (HbH)

20
Q

What is the management for beta thalassaemia intermedia and HbH disease?

A

Occasional transfusions

21
Q

What is the management for beta thalassaemia major?

A

Lifelong regular transfusions

–> maintain Hb 95-105

22
Q

What is the main cause of mortality in beta thalassaemia major?

A

Iron overload from regular transfusions

23
Q

How is iron overload managed in thalassaemia?

A

Iron chelating drugs e.g. desferrioxamine (SC/IV)

venesection not possible as patient is already anaemic

24
Q

Which side effects of iron chelating drugs is it important to monitor closely for?

A

Hearing and vision loss

25
Q

What is the pathophysiology behind ‘sickling’?

A

Recessive mutation in gene for beta-globin –> HbS (altered structure)
HbS polymerises if exposed to low oxygen levels for a prolonged period –> distorted shape of red cell

26
Q

What are the consequences of HbS red cells?

A

Breakdown easily –> haemolytic anaemia
Occlude the microvasculature
Are sequestered in liver + spleen –> splenic dysfunction + immunosuppression

27
Q

What is the lifespan of a HbS red cell?

A

20 days (HbA is 120 days)

28
Q

What are the features of sickle cell trait?

A

Asymptomatic carrier

May sickle in severe hypoxia e.g. high altitude, under anaesthesia

29
Q

What would be seen on the blood film and electrophoresis in sickle cell trait?

A

Film normal

Mainly HbA, HbS < 50%

30
Q

Which parts of the world have the highest rates of sickle cell anaemia?

A

Afro-Caribbean
Middle East
Mediterranean
Indian

31
Q

How would sickle cell anaemia appear of electrophoresis?

A

HbS > 80%, no HbA

32
Q

What are the chronic features of sickle cell anaemia?

A

Haemolytic anaemia: pallor, fatigue, jaundice
Chronic pain
Painful dactylitis (in age 6-18 months)
Splenomegaly
Hyposplenism due to repeated infarcts
Pigment gallstones from chronic haemolysis (affects 70%)
Raised CO –> systolic murmur + cardiomegaly

33
Q

What is a sickle cell crisis?

A

Episode of tissue infarction due to vascular occlusion

34
Q

What might trigger a sickly cell crisis?

A 
Cold
Dehydration
Stress
Infection
Pregnancy
Acidosis
Hypoxia
35
Q

Give some examples of symptoms of sickle cell crisis?

A

Acute painful limb, abdomen or chest
Stroke
Visual floaters
Chest pain + pneumonia –> acute chest syndrome (common in kids)

36
Q

Which type of infection may precipitate an aplastic crisis in a patient with sickle cell anaemia?

A

Parovirus B19

37
Q

Which type of infections are sickle cell patients particularly susceptible to?

A

Encapsulated bacteria –> due to hyposplenism (spleen responsible for removing encapsulated bacteria)

38
Q

How is sickle cell disease diagnosed?

A

Electrophoresis
High performance liquid chromatography (HPLC)
Hb isoelectric focusing (IEF)

39
Q

What is the general management of sickle cell anaemia?

A

Avoid alcohol + smoking
Prophylactic penicillin + all vaccinations
Folic acid supplements (especially in pregnancy)
Transfusions if symptomatic anaemia
Splenectomy if 2 sequestration crises
Hydroxycarbamide can reduce severity by inducing HbF production

40
Q

How is a sickle cell crisis treated?

A 
Opiates
Hydration
Rest
Oxygen
Antibiotics if infection
Red cell exchange transfusion if chest crisis or stroke
41
Q

How are haemoglobinopathies screened for?

A

Antenatal screening to identify carriers

  • family origin questionaire + FBC
  • further testing if from high risk area or abnormal red cell indices

Haematology (15 decks)

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