An improved technique for
bilirubin analysis, using high-performance liquid chromatography, has enabled us to study the occurrence and significance of four species of
bilirubin (unconjugated, monoconjugated, diconjugated, and
delta bilirubin) in 40 infants with
jaundice of various etiologies. We found that: (a) infants with indirect
hyperbilirubinemia showed greater than 90% of their total serum
bilirubin as unconjugated
bilirubin. The small remaining fraction consisted of conjugated
bilirubin; predominantly
delta bilirubin (5%); (b) infants with elevated direct serum
bilirubin (greater than or equal to 2 mg/dl) showed almost twice more monoconjugated than diconjugated
bilirubin fractions; (c) the standard diazo test for
bilirubin analysis underestimates the direct
bilirubin by as much as 34%; and (d)
delta bilirubin, a tightly
protein bound
bilirubin, was observed in significant amounts in infants with elevated direct
bilirubin. Its concentration, which ranged from 10-73% of the total
bilirubin, was related to the duration rather than to the cause of the
jaundice. It was also observed at birth in an infant with
giant-cell hepatitis. It is concluded that the identification of more specific
bilirubin species in jaundiced infants, especially in those with elevated direct serum
bilirubin, will further help in the understanding and management of their disease.