Haemolytic anaemia - PNH type II cells presenting a diagnostic dilemma

A 28-year-old man presented with a history of intermittent haematuria over the past 10 years usually following fever episodes and requiring blood transfusions during the episodes. History of any thrombotic complications, chest pain or erectile dysfunction was not forthcoming. Examination revealed severe pallor with mild icterus and mild splenomegaly. His blood picture showed pancytopenia with elevated reticulocytes and indirect hyperbilirubinaemia. Indirect Coombs test was positive but direct was negative, serum lactate dehydrogenase was elevated and agglutinins were found to be of IgG type. Bone marrow showed a hypercellular marrow with myeloid and megakaryocytes suppressed. Donath-Landsteiner antibodies were found to be negative ruling out paroxysmal cold haemoglobinuria. Flow cytometry was performed with a suspicion of paroxysmal nocturnal haemoglobinuria (PNH) and was shown to be partially negative for CD59 but positive for CD55, a pattern consistent with type II PNH.