Review Note

A 44-year-old woman presents with recurrent fever, pallor, malaise and shortness of breath. She has noticed a petechial rash on her skin and small bruises on her arms. A blood test reveals a pancytopenia. During examination, you palpate a large spleen. Which investigation would differentiate between hypersplenism and aplastic anaemia?

• Reticulocyte test
• Direct Coombs test 
• Metabisulfite test
• Ham's test
• Osmotic fragility test
  

Reticulocyte test

The reticulocyte test (A) would show reduced counts in aplastic anaemia while it is raised in hypersplenism. The metabisulphite (C) can be added to blood smears to mimic accelerated deoxygenation. RBCs with high haemoglobin S concentrations undergo sickling in a reduced oxygen environment and therefore this is a useful test for sickle cell anaemia. Ham's test (D) is used to diagnose paroxysmal nocturnal haemoglobinuria. The direct Coomb's test (B) is used to investigate causes of autoimmune haemolytic anaemia. The osmotic fragility test (E) is used to investigate hereditary spherocytosis.

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