Alternate Names : Conjugated Bilirubin-Urine, Direct Bilirubin-Urine

Definition

This is a urine test that measures the amount of bilirubin.

Bilirubin metabolism begins with the breakdown of red blood cells (RBCs) by phagocytic cells (cells that consume and digest other cells). Hemoglobin is broken down to heme and globin. Heme is converted to bilirubin, which is then carried by albumin in the blood to the liver.

In the liver, most of the bilirubin is conjugated with glucuronic acid before it is excreted in the bile. Conjugated bilirubin is called direct bilirubin (DB), and unconjugated bilirubin is called indirect bilirubin (IB). Total bilirubin = DB + IB. Conjugated bilirubin is excreted into the bile by the liver and stored in the gall bladder or transferred directly to the small intestines.

Bilirubin is further metabolized by bacteria in the intestines to urobilins, which contribute to the color of the feces. A small percentage of these compounds are reabsorbed and eventually appear in the urine, where they are referred to as urobilinogen.