Conjugated bilirubin

What is conjugated bilirubin?

Conjugated bilirubin (also called direct bilirubin) is the form of bilirubin that has been processed in the liver. Bilirubin is formed when hemoglobin from old red blood cells is broken down. It is first transported to the liver in a water-insoluble form. In the liver, bilirubin is bound to glucuronic acid (conjugated) and then becomes water-soluble. The conjugated bilirubin is normally excreted with bile into the intestine, where it contributes to digestion and is further converted into substances that, among other things, affect the color of the stool.

Why is conjugated bilirubin analyzed?

Conjugated bilirubin is analyzed to assess the liver's excretory capacity and to detect effects on the biliary tract. The test is particularly useful in the investigation of jaundice and when there is suspicion that bile flow is affected. Together with other liver tests (for example ALP, GT, ALT/AST), conjugated bilirubin can help distinguish between different causes of elevated bilirubin and provide a more targeted picture of whether it is a liver disorder or a bile duct obstruction.

Reference range for Bilirubin, conjugated