Which bilirubin fraction is unconjugated and covalently bound to albumin?

Which bilirubin fraction is unconjugated and covalently bound to albumin?

• A. Alpha
• B. Beta
• C. Delta
• D. Gamma

Answer: (C)

Delta bilirubin is the bilirubin fraction that forms a covalent bond with albumin in the blood. This creates a stable albumin–bilirubin complex that remains in circulation longer because it is not freely soluble or easily excreted. While unconjugated bilirubin is carried in plasma non-covalently by albumin, the covalently bound form—that persistent, albumin-bound pigment—is delta bilirubin. So, the option that identifies a bilirubin fraction bound to albumin through a covalent bond corresponds to delta bilirubin. The phrasing about unconjugated and covalently bound is a bit unusual, but delta bilirubin is the covalent, albumin-bound form in contrast to the non-covalent transport of unconjugated bilirubin.

Delta bilirubin is the bilirubin fraction that forms a covalent bond with albumin in the blood. This creates a stable albumin–bilirubin complex that remains in circulation longer because it is not freely soluble or easily excreted. While unconjugated bilirubin is carried in plasma non-covalently by albumin, the covalently bound form—that persistent, albumin-bound pigment—is delta bilirubin. So, the option that identifies a bilirubin fraction bound to albumin through a covalent bond corresponds to delta bilirubin. The phrasing about unconjugated and covalently bound is a bit unusual, but delta bilirubin is the covalent, albumin-bound form in contrast to the non-covalent transport of unconjugated bilirubin.