Bilirubin, a product of hemoglobin catabolism, is characterized by its distinctive yellow pigment. Only conjugated bilirubin is excreted in urine. If bilirubin is elevated and is conjugated, it will be detected by the urine reagent strip. The presence of bilirubin in urine in detectable amounts is always abnormal.
Unconjugated bilirubin cannot be excreted by the kidneys because it is bound to albumin and is not soluble in water.