Pediatric emergency medicine trisk 0884 0884
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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 5 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 2 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
