Vitamin B12 deficiency in India: mean corpuscular volume is an unreliable screening parameter

Vitamin B12 deficiency is thought to be more common than was previously believed, but there are little data from India on this. It has protean clinical manifestations, and raised mean corpuscular volume (MCV) is commonly used by physicians as an indicator for megaloblastic anaemia caused by vitamin B12 deficiency. We evaluated the clinical profiles of our patients with vitamin B12 deficiency and tried to ascertain how useful MCV and the peripheral smear were in diagnosis.

We evaluated the clinical picture, haematology indices and peripheral smear findings of 117 patients with low vitamin B12 levels. Serum folic acid, ferritin values and biopsy findings of some patients were also assessed.

Patients were commonly detected to have reduced levels of serum vitamin B12 during the work-up for anaemia (n=45) or for neurological symptoms (n=31). Of the 94 cases in which smears were examined, 26 showed macrocytes and hypersegmented neutrophils were present in 24. Twentysix patients showed a raised MCV, 50 patients had an MCV within the reference range and 28 had low MCV. Pancytopenia was present in 5 patients. Concomitant iron deficiency, as judged by serum ferritin levels, was present in 18 patients.

Vitamin B12 deficiency is not uncommon in India. It is often diagnosed during the work-up for a haematological disorder or for neurological symptoms. MCV is unreliable as a screening parameter for the presumed diagnosis of macrocytic anaemia, which is associated with vitamin B12 deficiency.