The plasma clearance of injected doses of folic acid as an index of folic acid deficiency.

The folic acid clearance test of Chanarin (1958) has been studied in normal white subjects, patients with megaloblastic anaemia, healthy Bantu males, Bantu females, hospital patients without anaemia, and in patients with scurvy. The test clearly distinguishes patients with megaloblastic anaemia, where clearance from the plasma of injected folic acid is abnormally rapid, from normal subjects. The rate of clearance of folic acid is abnormally rapid both in vitamin B(12) and in folic acid deficiency. Rapid clearance of injected folic acid in patients with primary B(12) deficiency may be the result of a conditioned deficiency of folic acid. The test is sufficiently sensitive to detect body deficiency of folic acid before the development of anaemia. In patients with scurvy, folic acid is cleared from the plasma abnormally rapidly. It is suggested that this may be the result of an associated dietary deficiency of folic acid.