1. Rula Harb, MD* 2. Daniel W. Thomas, MD† 1. *Children’s Hospital of Los Angeles, Los Angeles, Calif 2. †Editorial Board After completing this article, readers should be able to: 1. Describe the metabolism of bilirubin. 2. Evaluate a child of any age who has conjugated hyperbilirubinemia. 3. Recognize the signs and symptoms of Wilson disease. Jaundice refers to yellow discoloration of the skin, sclera, mucous membranes, and body fluids. It is a common problem that can be the presenting sign for many disorders. The challenge for the physician is to identify patients who need additional evaluation. The differential diagnosis for jaundice is age-specific; this review addresses the causative conditions in infants beyond the newborn period, older children, and adolescents. 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 …
