Bilirubin Fractionation in Newborns: Do You Know the Difference?

Conjugated and direct bilirubin levels are not interchangeable. Newborns with conjugated bilirubin levels ≥ 2.0 mg/dL require further in-depth assessment for cholestatic disease.

Most infants with jaundice have elevated unconjugated bilirubin levels owing to hemolytic causes, but some infants have jaundice owing to cholestasis. Measurement of serum conjugated bilirubin (CB) or direct bilirubin (DB) is recommended to rule out cholestasis. However, CB and DB levels are not the same: CB is a measure of bilirubin that has been conjugated with glucuronic acid in the liver. DB is a measure of both CB and delta bilirubin, and therefore the levels are higher than CB levels. To examine the clinical significance of elevated CB levels, researchers retrospectively evaluated bilirubin measurements obtained within 2 weeks of birth in 66,431 full-term infants born in California from 1995 through 2004.

The 99th percentiles for CB an…

Reviewing Author

William P. Kanto, Jr.,, MD