Bilirubin (direct)
What it measures, and what changes the number.
Direct bilirubin is the portion of bilirubin that the liver has already processed, or conjugated, into a water-soluble form so it can be passed into bile. Bilirubin itself is a yellow pigment made when old red blood cells are broken down.
It is almost always reported next to total bilirubin. The difference between the two is often shown as indirect, or unconjugated, bilirubin. It is also read with liver enzymes such as ALT, AST, ALP and GGT to give a broader picture of how the liver and bile ducts are handling bilirubin.
Bilirubin breaks down when exposed to light, so samples are ideally protected from light before testing. Haemolysis in the tube can interfere with the result. The direct method also picks up a fraction bound to albumin, so direct and conjugated bilirubin are close but not identical. Labs may print it as Bilirrubina directa (conjugada).
Often read alongside: Bilirubin (total), ALT, AST, ALP, GGT