Severe Vitamin B12 deficiency with complications in an elderly patient: a case study of pancytopenia and haemolysis

Severe vitamin B12 deficiency can lead to pancytopenia, haemolysis and various systemic manifestations. This case report discussed the case of a 66-year-old male patient who had adhered to a strict vegetarian diet for 5 years and presented with symptoms of fatigue, pallor and leg pain. Laboratory tests revealed severe pancytopenia (haemoglobin 4.8 g/dL, white cell count 2630/µL, platelets 112 000/mm³), macrocytic anaemia (mean cell volume 118 fL) and elevated lactate dehydrogenase (5480 U/L). Serum vitamin B12 was critically low at 61 pg/mL and bone marrow aspiration confirmed megaloblastic erythropoiesis. Intramuscular vitamin B12 supplementation resulted in rapid clinical and haematologic improvement, with complete resolution of pancytopenia and indirect hyperbilirubinaemia within 2 weeks. This case underscores the importance of early recognition of vitamin B12 deficiency in patients with unexplained cytopenia and haemolysis, particularly in populations with restrictive dietary habits. The authors discuss vitamin B12 deficiency in clinical practice, emphasising the need for awareness among healthcare providers to prevent irreversible complications through timely intervention and appropriate dietary counselling.