Glucoronides are chemically reactive metabolites. In adults, with prolonged cholestasis especially if it is accompanied by renal failure, a fraction of the bilirubin conjugates readily non enzymatically and irreversibly with serum albumin to give yellow billiproteins in which bilirubin is covalently bound to albumin. This fraction increases with the duration of cholestasis and is designated as delta bilirubin.
Delta bilirubin retains its direct reading properties. As delta bilirubin is irreversibly bound to albumin it is not filtered at the glomerulus and its half life reflects that of albumin (14 days). Consequently it remains in plasma long after other bilirubin esters have been eliminated giving rise to conjugated hyperbilirubinemia in the absence of bilirubinuria and is particularly evident in the recovery phase of cholestasis.
Delta bilirubin = Total bilirubin- (Conjugated + Unconjugated bilirubin)
