Dependency of MCV and haemoglobin concentration on plasma vitamin B12 levels in relation to sex and age.

In a retrospective study of 872 men and 1474 women we determined the relationship between serum vitamin B12 concentration and mean values for Hb and MCV, which were known for 68% of the men and 72% of the women. In both sexes there was a distinct decrease in the mean Hb at serum vitamin B12 concentrations < 0.05 nmol/l. However, the mean MCV was already raised by 4-5 fl at serum vitamin B12 levels < 0.16 nmol/l in men and < 0.11 nmol/l in women, and the percentage of patients with macrocytosis (defined as MCV > 100 fl) also increased significantly at these levels. To find out whether these relationships were age-dependent, male and female patients were split into groups of 20-70 years old and older persons. The mean MCV in men aged 20-70 years increased at a serum vitamin B12 level < 0.16 nmol/l, whereas in older men an increase in mean MCV occurred only at vitamin B12 levels < 0.11 nmol/l. In women, the mean MCV for both age groups increased significantly at a serum vitamin B12 level < 0.11 nmol/l. We conclude that haematological signs of B12 deficiency arise at different serum vitamin B12 concentrations in men and women and that only in men is there an age dependency.