Sickle cell anaemia

Question 1

What is the inheritance pattern of sickle cell anaemia?

Answer 1

Autosomal recessive

Question 2

Briefly summarise what sickle cell anaemia is:

Answer 2

A production of abnormal haemoglobin results in vaso-occlusive crises

Question 3

What is the genetic abnormality that causes SC anaemia?

Answer 3

Amino acid substitution in the gene coding for the Beta chain (Glutamine -> Valine) at position 6 which means HbS if formed instead of HbA.

They still have HbA2 and HbF.

Question 4

What is the difference between homozygotes HbSS and heterozygotes HbAS?

Answer 4

Homozygotes - Sickle cell anaemia

Heterozygotes - Sickle cell trait. Causes no disability and protects from falciparum malaria.

Question 5

Do heterozygotes get symptoms?

Answer 5

They can get sickling in hypoxia eg unpressurised aircraft, anaesthesia

Question 6

What is the pathophysiology of how sickle cells form?

Answer 6

HbS polymerises when deoxygenated, causing RBC to deform, produce sickle cells.

These are fragile and haemolyse, and block small blood vessels.

Question 7

What investigations would you do to confirm sickle cell anaemia?

Answer 7

Confirm haemolytic anaemia is present:
- Low Hb
- Raised reticulocytes
- Raised bilirubin
Blood film:
- Sickle cells
- Target cells
Sickle solubility test:
- Positive (detects HbS is present)
Hb electrophoresis:
- Confirms diagnosis and distinguishes between HbAS and HbSS

Question 8

What is an aplastic crises?

Is treatment needed?

Answer 8

• Triggered by parvovirus
• Causes a sudden fall in Hb
• Usually self limiting <2wks, tranfusion may be needed

Question 9

What will happen to the reticulocyte count in an aplastic crises?

Answer 9

Reduced due to bone marrow failure

Question 10

What is a sequestration crises?

Answer 10

Sickling within organs such as the spleen or lungs causes pooling of blood, worsening the anaemia.

Question 11

What is the treatment for a sequestration crises?

Answer 11

Urgent blood transfusion

Question 12

What will happen to the reticulocyte count with a sequestration crises?

Answer 12

INCREASED

Question 13

What can trigger a vaso-occlusive ‘painful’ crises?

Answer 13

Cold, dehydration, infection, hypoxia

Question 14

How can a vaso-occlusive crises present?

Answer 14

• Mesenteric ischaemia
• Stroke, seizure
• Avascular necrosis of femoral head
• Priaprism

Question 15

What is acute chest syndrome?

Answer 15

Vaso-occlusion crises in the pulmonary microvasculature, leading to infarction in the lung parenchyma

Question 16

How can acute chest syndrome present?

Answer 16

• Dyspnoea
• Chest pain
• Pulmonary infiltrates on chest xray
• low pO2

Question 17

How do you manage acute chest syndrome?

Answer 17

1. Pain relief
2. O2 therapy
3. Antibiotics as infection may precipitate acute chest syndrome (cephalosporin + macrolide)
4. Blood transfusion to improve oxygenation
5. Consider bronchodilators

Question 18

What is a haemolytic crises?

Answer 18

Fall in Hb due to increased rate of haemolysis

Question 19

What complications occur with sickle cell anaemia?

Answer 19

1. Splenic infarction so increased risk of infections
2. Poor growth
3. Chronic renal failure
4. Gall stones
5. Retinal disease
6. Iron overload
7. Lung damage -> hypoxia -> Fibrosis -> Pulmonary hypertension

Question 20

What is the general management for sickle cell anaemia?

Answer 20

• Hydroxycarbamide (increases HbF)
• Hyposplenism -> Prophylactic antibiotics and imms
• Rescue outpatient antibiotics to prevent sepsis
• Bone marrow transplant (controversial)

Question 21

How do you manage a sickle cell crises?

Answer 21

1. Prompt generous analgesia (do they have a personalised analgesia plan?)
2. Crossmatch blood - FBC, reticulocytes
3. Temp? - septic screen (CXR, MSU, blood cultures)
4. Rehydrate with IV fluids and O2
5. Start antibiotics empirically if unwell
6. Measure PCV, reticulocytes, liver and spleen size twice daily.
7. Blood tranfusion
8. Refer to haematology

Question 22

How often do you give the pneumococcal vaccine?

Answer 22

Every 5 years