Severe megaloblastic bone marrow change associated with unsuspected mild vitamin B12 deficiency

Summary Two patients are reported who developed peripheral blood abnormalities and marked megaloblastic bone marrow change within eleven days of cardiac bypass surgery. The patients were shown to have unsuspected mild vitamin B₁₂ deficiency due to Addisonian pernicious anaemia. The megaloblastic changes were presumed to be precipitated by the increased demand for erythrocytes and platelets after surgery.