Brief Report: Vitamin B₁₂ and Folate Activity in Normal Human Platelets

The vitamin B₁₂ and folate content of human platelets have been determined. The B₁₂ concentration was sixfold that in red cells and one-sixth that in leukocytes. In normal whole blood, with a platelet count of 300,000 per cu. mm., the B₁₂ activity contributed by platelets would be 6-21 pg. per ml. The contribution of platelets to the folate activity of normal whole blood averaged 0.4-1.7 ng. per ml. The folate activity in platelets was one-fifth that in an equal volume of red cells, but unlike red cell folate, was not increased by incubating platelet extracts with plasma.