Urinary urobilinogen determined by a mercuric chloride procedure.

In this quantitative assay, urinary urobilinogen is oxidized to urobilin with iodate in an acid medium, the pH is adjusted to 6 with sodium acetate, and the mixture is reacted with alcoholic HgCl2 solution, extracted with CHCl3, the measured spectrophotometrically at 513 nm. The artificial standards of previous methods have been replaced with crystalline stercobilin IX (commercially available), a urobilin closely related to the urinary urobilins. The reproducibility of the method, as assessed from 10 replicates of a single urine specimen to which urobilinogen was added, gave a coefficient of variation of 3.9%. Analytical recovery of urobilinogen added to urines was 90.4% (SD 14.5%). Bilirubin, biliverdin, mesobilirubin, coproporphyrin I, uroporphyrin I, and porphobilinogen do not interfere.