Bicytopenia with haemolysis: Think severe vitamin B12 deficiency-associated thrombotic microangiopathy

Bicytopenia is not uncommonly encountered in clinical practice; it may reflect either marrow failure or a consumptive process such as haemolysis with thrombotic microangiopathy (TMA). We describe a case of a patient with bicytopenia caused by severe Vitamin B12 deficiency, where there is laboratory evidence that is suggestive of haemolysis in what is known as pseudo-TMA phenomenon. Lack of awareness of this entity may lead clinicians to misdiagnose such cases as microangiopathic haemolytic anaemia (MAHA) or thrombotic thrombocytopenic purpura (TTP), which could lead to inappropriate immunomodulatory treatment or plasmapheresis being administered. To distinguish between true MAHA/TTP and pseudo-TMA from severe vitamin B12 deficiency, reticulocyte and vitamin B12 levels are useful tests in the first instance, while ADAMTS13 activity is the definitive test to diagnose TTP if suspected.