Relative importance of formiminoglutamic and urocanic acid excretion after a histidine load.

A thin-layer chromatographic method for the simultaneous assessment of formimino-glutamic (Figlu) and urocanic acid excretion after loading with 15 g. histidine has been applied to 15 control subjects and to 49 selected patients. Upper limits of normal excretion were determined for urocanic acid and Figlu alone (15 mg. and 30 mg/8 hr. respectively), and for the combined metabolites (40 mg./8 hr.). Of the 49 patients studied, 27 excreted total metabolites above 40 mg./8 hr.; of these 19 would have been revealed by their abnormal excretion of Figlu and 22 by their abnormal excretion of urocanic acid. Of 74 tests in the 64 subjects, urocanic acid was present in all but 27% of the tests, and in 29.8% of the tests urocanic acid was in excess of the amount of Figlu excreted. In six normal and six abnormal tests urocanic acid was the sole metabolite present. These results re-emphasize the value of estimating both histidine metabolites in tests for folate deficiency in man, and underline the greater relative importance of urocanic acid.