Direct Bilirubin Test

A serum direct (conjugated) bilirubin test measures the amount of bilirubin that has been processed in the bile and conjugated to glucuronic acid, making it water-soluble and excreted in bile. This test is usually ordered along with total bilirubin to help differentiate between the causes of hyperbilirubinemia, as elevated levels primarily indicate liver disorders or bile duct obstruction (obstructive jaundice).