Bilirubinuria Causes and Evaluation

Introduction to Bilirubin Metabolism

The presence of bilirubin in urine is primarily caused by conjugated hyperbilirubinemia, which results from liver parenchymal disease or obstruction of the biliary system, as noted by the American Gastroenterological Association 1, 2
Bilirubin exists in two forms: unconjugated (indirect) bilirubin, an insoluble form transported to the liver, and conjugated (direct) bilirubin, a soluble form that can be excreted, according to the American Association for the Study of Liver Diseases 1
Only conjugated bilirubin appears in urine, as unconjugated bilirubin is bound to albumin and too large to be filtered by the kidneys, as stated by the American College of Radiology 1, 2

Hepatic inflammation disrupting conjugated bilirubin transport can be caused by viral hepatitis, alcohol-induced liver disease, autoimmune hepatitis, and drug-induced liver injury from medications such as acetaminophen, penicillin, oral contraceptives, estrogenic or anabolic steroids, and chlorpromazine, as reported by the American College of Radiology 2
Cholestatic liver diseases, including primary biliary cholangitis, primary sclerosing cholangitis, and hereditary cholestatic disorders, can also cause bilirubinuria, according to the Mayo Clinic 2, 3

Intrinsic biliary obstruction can be caused by cholelithiasis, acute calculus cholecystitis, choledocholithiasis, cholangitis, cholangiocarcinoma, and gallbladder cancer, as noted by the American College of Radiology 2
Extrinsic biliary obstruction can be caused by pancreatic tumors, pancreatitis, and diffuse malignancy, such as lymphoma, as reported by the American College of Radiology 2

Neonatal cholestasis, or jaundice due to conjugated bilirubin lasting >2-3 weeks after birth, can be caused by genetic and metabolic disorders, biliary atresia, and alpha-1-antitrypsin deficiency, according to the Mayo Clinic 3

The detection of bilirubin in urine indicates the presence of conjugated hyperbilirubinemia, as stated by the American Gastroenterological Association and the American College of Radiology 1, 2
Fractionation of total bilirubin should be performed to determine the percentage derived from direct bilirubin, as recommended by the European Association for the Study of the Liver 4
Elevated alkaline phosphatase (ALP) should be confirmed to be of hepatobiliary origin with gamma-glutamyl transferase (GGT) and/or ALP isoenzyme fractionation, as suggested by the American Association for the Study of Liver Diseases 4
Ultrasound is the most useful initial imaging modality, with a positive predictive value of 98% and sensitivity of 65-95% for liver parenchymal disease, as reported by the American College of Radiology 2

Confirm that bilirubin in urine is due to conjugated hyperbilirubinemia by measuring serum total and direct bilirubin, as recommended by the American Gastroenterological Association and the European Association for the Study of the Liver 1, 4
Evaluate for elevated liver enzymes (AST, ALT) and cholestatic markers (ALP, GGT), as suggested by the American Association for the Study of Liver Diseases and the American College of Gastroenterology 1, 7
Perform abdominal ultrasound to assess for biliary obstruction and liver parenchymal disease, as recommended by the American College of Radiology 2
Consider further imaging (MRI, ERCP) if a dominant biliary stricture is suspected, as suggested by the European Association for the Study of the Liver 4