Excessively high serum vitamin B12 level in patients with a provisional diagnosis of megaloblastic anemia.

ABSTRACT

High serum vitamin B12 level has been reported in patients with liver diseases ad some hematological disorders. It has been observed that some patients diagnosed as megaloblastic anemia have high serum vitamin B12 with low serum unsaturated vitamin B12 binding capacity (UBBC). The objective of the present study was to investigate in these patients. A retrospective study in 9 patients with a provisional diagnosis of megaloblastic anemia showed extraordinarily high serum vitamin B12 with very low UBBC. Their past history showed that these patients were treated with 1,000 g vitamin B12 intramuscularly 10-24 hours before serum samples were taken for vitamin B12 determination. Study in another 3 patients showed that within 12 hours after a single injection of 1,000 g cyanocobalamin, their serum vitamin B12 raised considerably with an extremely low UBBC level. These findings indicated that the injected vitamin B12 saturated all transcobalamins and then exceeded to bind to other serum proteins such as albumin and gamma globulin. Serum vitamin B12 was maintained at a very high level with a very low unsaturated vitamin B12 binding capacity. Therefore the past history of receiving vitamin B12 must be exactly known in any patients who were taken blood sample for vitamin B12 determination.