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 >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 (≥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.
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