Which type of bilirubin is unconjugated (indirect)?

Which type of bilirubin is unconjugated (indirect)?

• A. Direct
• B. Delta
• C. Indirect
• D. Mixed

Answer: (C)

Unconjugated (indirect) bilirubin is the form produced from heme breakdown that has not yet been processed by the liver’s glucuronidation step. It’s lipid-soluble and travels in the bloodstream bound to albumin, since it isn’t water-soluble enough to be excreted. It only becomes direct (conjugated) bilirubin after the liver adds glucuronic acid, making it water-soluble and excretable into bile. Delta bilirubin is conjugated bilirubin still attached to albumin, and direct bilirubin is the conjugated form itself. So the type that is unconjugated is the indirect bilirubin. This distinction matters clinically because unconjugated bilirubin rises with increased production or impaired hepatic uptake (e.g., hemolysis, Gilbert syndrome), while conjugated bilirubin rises with problems in bile flow (e.g., cholestasis).

Unconjugated (indirect) bilirubin is the form produced from heme breakdown that has not yet been processed by the liver’s glucuronidation step. It’s lipid-soluble and travels in the bloodstream bound to albumin, since it isn’t water-soluble enough to be excreted. It only becomes direct (conjugated) bilirubin after the liver adds glucuronic acid, making it water-soluble and excretable into bile. Delta bilirubin is conjugated bilirubin still attached to albumin, and direct bilirubin is the conjugated form itself. So the type that is unconjugated is the indirect bilirubin. This distinction matters clinically because unconjugated bilirubin rises with increased production or impaired hepatic uptake (e.g., hemolysis, Gilbert syndrome), while conjugated bilirubin rises with problems in bile flow (e.g., cholestasis).