Bilirubinuria

Abstract

Bilirubinuria is the presence of bilirubin in the urine. It can be detected by the standardized urine dipstick, mostly referred to as urinalysis in most hospitals worldwide. Bilirubin and related breakdown metabolites are well known for causing the characteristic coloring in bile and stool; however, its presence in the urine is not normal, and for it to be present there, it must be water-soluble and excreted by the kidney. Bilirubin in the body exists as either conjugated/direct or unconjugated/indirect. Unconjugated bilirubin is soluble in fat but insoluble in water and thus cannot be renally excreted. Unconjugated hyperbilirubinemia is characterized by acholuric jaundice as urine is not darkened by urinary bilirubin as bilirubin is not detected in the urine in such cases. On the other hand, conjugated bilirubin is water-soluble and thus can be renally excreted and detected in the urine. Patients may describe their urine as tea or cola-colored when they have jaundice and conjugated hyperbilirubinemia due to liver or biliary disease. In a healthy individual with normal liver function and bile duct anatomy, bilirubin is not detectable in the urine. Therefore, bilirubinuria is a marker of conjugated hyperbilirubinemia and can be the earliest sign of hepatic or biliary disease.