 Furthermore, direct bilirubin tends to overestimate conjugated bilirubin levels due to unconjugated bilirubin that has reacted with diazosulfanilic acid, leading to increased azobilirubin levels (and increased direct bilirubin).δ bilirubin = total bilirubin – (unconjugated bilirubin + conjugated bilirubin)

The half-life of delta bilirubin is equivalent to that of albumin since the former is bound to the latter, yields 2–3 weeks.A free-of-bound bilirubin has a half-life of 2 to 4 hours.