The test for bilirubin on the urine chemical reagent strip is based on the formation of an azo dye resulting from a reaction of bilirubin with a diazonium salt in an acid medium. The color of this dye 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 the positive or negative color blocks on the color chart may be due to bilirubin-derived bile pigments. Any urine demonstrating an atypical color on the bilirubin test strip should be tested further. Even a slight color change should be considered significant since bilirubin is never present in normal urine.
