Which expression best describes the bilirubin fraction Delta?

Which expression best describes the bilirubin fraction Delta?

• A. Delta is conjugated bilirubin soluble in plasma
• B. Delta is unconjugated bilirubin covalently bound to albumin
• C. Delta is unconjugated bilirubin not bound to any protein
• D. Delta is conjugated bilirubin covalently bound to albumin

Answer: (B)

Delta bilirubin is the bilirubin fraction that remains in the blood as a covalently bound complex with albumin. This means the bilirubin involved comes from the unconjugated pool, but its defining feature is a covalent attachment to albumin, not glucuronidation. The covalent link to albumin makes it effectively nonexchangeable and long-lasting, so it persists in circulation longer than the other fractions. This explains why delta bilirubin can stay elevated even after other bilirubin levels fall.

Delta bilirubin is the bilirubin fraction that remains in the blood as a covalently bound complex with albumin. This means the bilirubin involved comes from the unconjugated pool, but its defining feature is a covalent attachment to albumin, not glucuronidation. The covalent link to albumin makes it effectively nonexchangeable and long-lasting, so it persists in circulation longer than the other fractions. This explains why delta bilirubin can stay elevated even after other bilirubin levels fall.