CHAPTER 45 ■ JAUNDICE: UNCONJUGATED HYPERBILIRUBINEMIA DANA ARONSON SCHINASI INTRODUCTION Jaundice is a yellowish discoloration of the skin, tissues, and bodily fluids that results from the deposition of unconjugated bilirubin pigment in the skin and mucous membranes It is estimated that 60% to 80% of all term newborns develop jaundice Hyperbilirubinemia refers to a serum bilirubin level greater than mg/dL; unconjugated (indirect) hyperbilirubinemia is the most common form of jaundice encountered by emergency department (ED) practitioners In conjugated (direct) hyperbilirubinemia, the conjugated fraction exceeds mg/dL or is greater than 20% of the total serum bilirubin (TSB) (see Chapter 44 Jaundice: Conjugated Hyperbilirubinemia ) Clinicians must follow a systematic approach to distinguish between the physiologic and pathologic etiologies of unconjugated hyperbilirubinemia in order to promptly identify children in need of immediate intervention The ultimate goal is to prevent the development of bilirubin-induced neurologic dysfunction (BIND), a spectrum of neurologic findings and sequelae ranging from subtle manifestations to kernicterus, the permanent neurologic consequence of bilirubin deposition in brain tissue; population studies indicate that the incidence of kernicterus is decreasing PATHOPHYSIOLOGY Bilirubin is the final product of heme degradation Heme protoporphyrin is oxidized and subsequently reduced in macrophages to form unconjugated bilirubin, which is released into the plasma At physiologic pH, bilirubin is insoluble in plasma and requires binding to albumin When it exceeds the binding capacity of albumin, the unbound unconjugated bilirubin may cross the blood– brain barrier and deposit in the basal ganglia, causing acute bilirubin encephalopathy (ABE) During normal physiologic conditions, the liver conjugates bilirubin by glucuronyl transferase and subsequently excretes the conjugated form into bile Most conjugated bilirubin is secreted through the bile into the small intestine, where bacterial enzymes degrade it to urobilinogen; 90% is degraded and