A 54-year-old woman recovering from a month of extrahepatic biliary obstruction has a falling alkaline phosphatase, yet her direct-reacting bilirubin remains 6 mg/dL despite clinical improvement and near-normal conjugated bilirubin on chromatography. The MOST likely explanation is:
- A Delta bilirubin, a covalent complex of conjugated bilirubin with albumin, which clears with the albumin half-life ✓
- B Ongoing hepatocellular necrosis releasing stored bilirubin
- C Recurrent obstruction at the ampulla of Vater
- D Conversion of unconjugated bilirubin to conjugated form within plasma
Correct answer: A. Delta bilirubin, a covalent complex of conjugated bilirubin with albumin, which clears with the albumin half-life
Explanation
In prolonged cholestasis, a fraction of conjugated bilirubin forms a covalent bond with albumin, producing delta bilirubin. Because it is albumin-bound it cannot be filtered by the kidney and disappears only with albumin turnover, giving a half-life of 12 to 14 days. This explains persistent direct-reacting hyperbilirubinemia during recovery when true conjugated bilirubin has already normalized. It is detected by the van den Bergh reaction as direct bilirubin, misleading clinicians who expect rapid clearing.
Reference: Harper's Illustrated Biochemistry, 32nd ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.