Severe vitamin B₁₂ deficiency in a 15-year-old boy: presentation with haemolysis and pancytopenia.

A 15-year-old boy on a vegetarian diet presented with severe macrocytic anaemia (haemoglobin, 5.1 g/dL; mean corpuscular volume, 116 fL) in addition to leucopenia and thrombocytopaenia (pancytopenia), icterus secondary to haemolysis and splenomegaly. Laboratory investigations revealed severe vitamin B12 (cobalamin) deficiency. Following cobalamin replacement therapy, the patient reported increased well-being, including appetite and weight gain, and his icterus resolved. In the follow-up laboratory examinations, leucocyte and platelet counts in addition to serum bilirubin and lactate dehydrogenase levels normalised. At the end of 2 months, laboratory findings, including haemoglobin level, were all within the normal range. We present this case as a reminder that severe vitamin B12 deficiency may present with findings mimicking acute leukaemia (pancytopenia and splenomegaly) and findings suggestive of pseudothrombotic microangiopathy.