A False-Positive Test for Bile

Abstract

To the Editor.— I have recently had an interesting experience with a falsepositive test for bile with the BiliLabstix (Ames Co.). It turned out that the patient had acute intermittent porphyria, and I feel certain that the false-positive results were due to the presence of porphobilinogen; quantitative studies showed 137.0 mg of porphobilinogen in 24 hours (normal, 0 to 4 mg). The portion of the strip that tests for bile contains two reagents: dichloraniline diazonium salt for testing for bilirubin, and p -dimethylaminobenzaldehyde for testing for urobilinogen. The latter, of course, is the active reagent in Ehrlich aldehyde in the Watson-Schwartz test that reacts with both urobilinogen and porphobilinogen to produce a red color. To complete the Watson-Schwartz reaction, an organic solvent is needed to separate the urobilinogen aldehyde from the porphobilinogen. My purpose in calling this to your attention is to alert physicians to the possibility of acute intermittent