Summary

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.