Haematology >
Sickle Cell Anaemia

“Autosomal recessive disorder in which production of abnormal haemoglobin results in vaso-occlusive crises”

  • HbSS- homozygotes, have sickle cell disease
  • HbAS- heterozygotes, have sickle cell trait
Risk Factors
  • Most commonly in people of African origin (1:700 people of African descent)
  • Family history (parents with sickle cell trait
Aetiology
  • Amino acid substitution in the gene coding for the β chain (Glu → Val at position 6) leading to the production of HbS instead of HbA
Pathophysiology
  • HbS polymerizes when deoxygenated → RBCs to deform → produces sickle cells which are fragile and haemolyse, also block small vessels
Clinical Presentation
  • Symptoms:
    • Lethargy and general weakness
    • Growth restriction
    • Episodes of pain
    • Swelling of hands and feet
    • Frequent infections
    • Vision problems
  • Signs:
    • Jaundice
    • Pallor
    • Delayed puberty
Sickle Cell Crisis
  • Vaso-occlusive crises
    • Most common crisis
    • Precipitated by cold, infection, dehydration, exertion, ischaemia
    • Occlusion of small vessels
    • Swollen painful joints, tachypnoea, acute abdominal distension and pain, loin pain, retinal occlusion
    • Large vessels à stroke, acute sickle chest syndrome, placental infarction
    • Acute chest syndrome- vaso-occlusive in the lungs, infections in children, infarcts in adults
  • Aplastic crisis
    • Temporary cessation of erythropoiesis causing severe anaemia
    • Usually caused by infection with parvovirus B19
    • Drop-in Hb
    • Spontaneous recovery but may require a transfusion
  • Sequestration crisis
    • Sudden enlargement of the spleen
    • The pooling of blood in spleen ± liver with severe anaemia
    • Urgent transfusion needed
Investigations
  • FBC
  • Blood film
  • Sickle solubility test
  • Hb electrophoresis
  • Other tests:
    • Renal function tests
    • LFTs
    • Lung function tests
Management
  • Neonatal screening for sickle cell disease
  • Conservative:
    • Parental and patient education
    • Avoid triggers of crises- cold, dehydration, exhaustion
    • Avoid alcohol and smoking
  • Medical:
    • Hydroxycarbamide (hydroxyurea)
    • Folic acid supplementation
    • Zinc supplementation if growth is restricted
    • Vit D supplementation especially in non-white children in the UK
    • Oral penicillin prophylaxis started at diagnosis
    • Routine childhood vaccinations
    • Malaria chemoprophylaxis (malaria significant cause of morbidity and mortality in patients)
    • Blood transfusion therapy in severe anaemia
  • Surgical:
    • Bone marrow transplantation only in severe disease and a matched sibling donor
  • Prevention:
    • Genetic counselling
    • Prenatal tests
Complications
  • Splenic infarction before 2 years old → increased susceptibility to infection
  • Poor growth
  • Chronic renal failure
  • Gallstones due to chronic haemolytic anaemia
  • Eye- retinopathy, retinal infarcts, retinal haemorrhage, retinal detachment
  • Stroke
  • Chronic pain
  • Nocturnal enuresis
  • Iron overload
  • Leg ulcers Lung damage → hypoxia → fibrosis → pulmonary hypertension

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