The test for bilirubin on the urine chemical reagent strip is based on the formation of an azobilirubin compound resulting from a reaction of bilirubin in an acid medium with diazotized 2, 4 dichloroaniline. The color of this compound ranges through various shades of tan. Some sources describe the colors produced as shades of tan-to-pink-to-violet.
Since other pigments in the urine may influence the test results, this test is more difficult to interpret than other urine reagent strip tests. Colors that are unlike either the positive or negative color blocks on the color chart may be due to the presence of bilirubin-derived bile pigments. Any urine that demonstrates an atypical color on the bilirubin test strip should be tested further. Even a slight change in color should be considered significant since bilirubin is never present in normal urine.
