Endotoxemia and hyperbilirubinemia in the neonate.

One hundred twenty-five neonates with varying serum bilirubin levels were tested for endotoxin by the limulus amebocyte lysate (LAL) test. Neither infection nor hemolytic disease was a contributing factor to the bilirubin levels. As the serum bilirubin level rose, positive LAL tests increased in frequency until the LAL test attained 100% at a level of 13 mg/dL. Bilirubin at different concentrations did not elicit positive LAL tests in plasma or normal saline in vitro. The LAL test was positive in urine obtained by suprapubic aspiration in 50% of neonates with positive serum LAL tests. Although bilirubin and endotoxin are cleared independently by hepatic cells with different functions, a striking relationship is evident between the endotoxin and bilirubin levels in the neonate. Immaturity of physiological liver functions in the neonate plays an important role. The LAL test cannot be used as an indicator of Gram-negative sepsis in neonates with unconjugated hyperbilirubinemia.