Unconjugated Hyperbilirubinemia

Excerpt

Hyperbilirubinemia is a condition defined as elevated serum or plasma bilirubin levels above the reference range of the laboratory, and it is due to disorders of bilirubin metabolism. Depending on the form of bilirubin present in serum, hyperbilirubinemia can be further classified as unconjugated (indirect) or conjugated (direct). Unconjugated hyperbilirubinemia (albumin-bound) usually results from increased production, impaired hepatic uptake, and decreased conjugation of bilirubin. In neonates, jaundice typically occurs due to unconjugated hyperbilirubinemia, which is characterized by the increased levels of indirect or unconjugated bilirubin (UCB) in the serum. In newborns, the increased concentration of UCB can cross the blood-brain barrier, and deposit in the basal ganglia or cerebellum causing a bilirubin-induced encephalopathy or kernicterus. Several inherited disorders can also produce unconjugated hyperbilirubinemia, including Gilbert syndrome, Crigler-Najjar syndromes type I and II, and inherited disorders causing hemolytic anemia.