Test Details: This test is used to confirm suspected diagnosis of Gilbert syndrome or Crigler-Najjar syndrome. Crigler-Najjar syndrome is a rare, autosomal recessive disorder resulting from severe functional deficiency of hepatic UGT1A1 enzyme and characterized by intermediate to severe hyperbilirubinemia, jaundice and risk for kernicterus. Gilbert syndrome is a common inherited condition resulting from a mild decrease in UGT1A1 activity and individuals may be asymptomatic or have mild, fluctuating hyperbilirubinemia and intermittent jaundice.