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Jaundice is defined by a serum bilirubin concentration greater than 5 mg/dL. Clinical jaundice develops in 50% of newborns, and breast-feed infants have an increased incidence of jaundice. Differentiation between physiologic jaundice, which is seen in many infants during the first week of life, and pathologic jaundice is essential because pathologic jaundice is a sign of a more serious condition.
Pathophysiology
Physiologic Versus Pathologic Jaundice
Physiologic jaundice is characterized by unconjugated hyperbilirubinemia that peaks by the third or fourth day of life in full-term newborns and then steadily declines by 1 week of age. Asian newborns tend to have higher peak bilirubin concentrations and more prolonged jaundice. Premature infants are more likely to develop jaundice.
Causes of Physiologic Jaundice
Increased bilirubin load due to the high red blood cell volume in newborns and shortened blood cell survival.
Deficient hepatic uptake and deficient conjugation of bilirubin.
Increased enterohepatic bilirubin reabsorption.
Deficient excretion of bilirubin.
Pathologic jaundice usually appears within the first 24 hours after birth and is characterized by a rapidly rising serum bilirubin concentration (>5 mg/dL per day), prolonged jaundice (>7 to 10 days in a full-term infant), or an elevated direct bilirubin concentration (>2 mg/dL or more than 20% of total serum bilirubin). Conjugated hyperbilirubinemia never has a physiologic cause and must always be investigated.