A microbiologic method for detecting folic acid deficiency in man.

EARLY ALL MICROBIOLOGIC assays for folic acid activity (FA) have used Streptococcus faecalis and Lactobacillus casei (1). Earlier it appeared that these organisms could not detect FA deficiency in man (2, 3); for example, in one study using S. faecalis there was no detectible activity in the fasting serum of humans (4). Administration of a loading dose of folic acid with subsequent assay by S. faecalis (5) has served as a workable means of determining FA deficiency (6), a technic having definite drawbacks (7). An indirect method for detecting FA deficiency based on the excretion of formimino-L-glutamic acid (FIG1u), an intermediate in the catabolism of histidine, has been reported (8, 9, 10). Although this method seems to be generally accepted, there have been reported instances of vitamin B12 deficiency in which FIG1u excretion was demonstrated and cases of FA deficiency in which FIG1u was not excreted (11). The method, therefore, is not dependable for detecting FA deficiency in man. This report presents a microbiologic assay for FA activity in human serum which agrees with the clinical FA status (11).