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(Pediatrics in Review. 2007;28:83-91.)
© 2007 American Academy of Pediatrics

Editorial Board
| The first 300 words of the full text of this article appear below. |
| Objectives |
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| Introduction |
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Jaundice is caused by elevated serum bilirubin concentrations. It is apparent in infants when the serum bilirubin value is greater than 4 to 5 mg/dL (68.4 to 85.5 mcmol/L) and in older children at values greater than 2 to 3 mg/dL (34.2 to 51.3 mmol/L). Serum total bilirubin is measured in the laboratory as the sum of two components: unconjugated ("indirect") and conjugated ("direct") fractions. The terms "direct" and conjugated hyperbilirubinemia often are used interchangeably. However, this usage is not always accurate because direct bilirubin may include both the conjugated fraction and bilirubin bound to albumin (delta bilirubin). Delta bilirubin is formed by covalent bonding between conjugated bilirubin in the serum and albumin; it is metabolized with albumin and has a similar half-life of 21 days. The presence of delta bilirubin often prolongs direct hyperbilirubinemia while results of the other liver tests are normalizing. Many hospitals continue to measure direct bilirubin by a method that includes both direct and delta bilirubin. Clinicians should consider asking for a breakdown of the direct bilirubin fraction if the jaundice is prolonged or presenting atypically.
Conjugated hyperbilirubinemia is defined as a conjugated bilirubin concentration greater than 2 mg/dL (34.2 mmol/L) or more than 20% of total bilirubin. It
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