INTRODUCTION AND DEFINITIONS
Almost all newborn infants develop a total serum or plasma bilirubin (TB) level greater than 1 mg/dL (17 micromol/L), which is the upper limit of normal for adults. As TB increases, it produces neonatal jaundice, the yellowish discoloration of the skin and/or sclerae caused by bilirubin deposition . (See "Clinical manifestations of unconjugated hyperbilirubinemia in term and late preterm infants", section on 'Jaundice'.)
Hyperbilirubinemia in infants ≥35 weeks gestation is defined as a TB >95th percentile for hours of age on the Bhutani nomogram . Hyperbilirubinemia with a TB >25 to 30 mg/dL (428 to 513 micromol/L) is associated with an increased risk for bilirubin-induced neurologic dysfunction (BIND) (figure 1), which occurs when bilirubin crosses the blood-brain barrier and binds to brain tissue. The term "acute bilirubin encephalopathy" (ABE) is used to describe the acute manifestations of BIND, while the term "kernicterus" is used to describe the chronic and permanent sequelae of BIND.
Appropriate intervention is important to consider in every infant with severe hyperbilirubinemia. However, even if these infants are adequately treated, long-term neurologic sequelae (kernicterus) can sometimes develop. (See "Clinical manifestations of unconjugated hyperbilirubinemia in term and late preterm infants", section on 'Neurologic manifestations'.)
The evaluation of neonatal unconjugated hyperbilirubinemia is reviewed here. The pathogenesis, etiology, clinical manifestations, and treatment of hyperbilirubinemia are discussed separately. (See "Pathogenesis and etiology of unconjugated hyperbilirubinemia in the newborn" and "Clinical manifestations of unconjugated hyperbilirubinemia in term and late preterm infants" and "Treatment of unconjugated hyperbilirubinemia in term and late preterm infants".)
Two advances in medical care had a significant impact on the need for treatment and the way in which hyperbilirubinemia is managed. The administration of Rh (D) immunoglobulin to Rh-negative mothers in the late 1960s dramatically decreased the incidence of neonatal Rh isoimmune hemolytic disease. At about the same time, the introduction of phototherapy in the United States significantly reduced the need for exchange transfusions and the risk of severe hyperbilirubinemia. Thus, the risk of kernicterus was reduced from its peak in the 1950s through the 1970s. Nevertheless, isolated cases of kernicterus, a preventable condition, continue to be reported [2-4].