The reagent strip test for bilirubin is based on the coupling of a diazonium salt with bilirubin. Secondary (confirmatory) methods that are currently available are also based on the coupling of a diazonium salt with bilirubin. However, these tests are more sensitive than the reagent strip method and less prone to color interference from large amounts of blood in the urine, very concentrated urine, or drugs that discolor the urine, such as phenazopyridine (Pyridium). Confirmation of reagent strip bilirubin results with a secondary method should be performed if color interference is a possibility to prevent reporting of a false-positive result.
Secondary methods use a reagent tablet or disk, which is placed on a test pad. When the reagent comes in contact with urine containing bilirubin, a blue to purple color is produced on the test pad.
