Abstract 1335 Poster Session IV, Tuesday, 5/4 (poster 360)

Neonatal hyperbilirubinemia occurs when production exceeds elimination of bilirubin. While either increased bilirubin production or decreased elimination may be a factor in the hyperbilirubinemic neonate, how frequently elevated bilirubin production is a predominant factor in hyperbilirubinemia is unclear. Because carbon monoxide (CO) and bilirubin are produced in equimolar amounts during heme degradation, the end-tidal CO concentration corrected for inhaled CO (ETCOc) can provide a useful index of the rate bilirubin production. A timed serum total bilirubin (STB) can serve as an index of elimination. In this study, the ETCOc and STB were measured 30 ± 6h after birth. STB was subsequently measured at 96 ± 12h for all subjects, and more frequently if clinically indicated. Subjects with elevated TSB at 96 ± 12h had subsequent periodic STB measurements taken until STB levels began to fall, or until phototherapy was initiated. A subject was defined as hyperbilirubinemic if their STB exceeded the 95th percentile, as defined by a bilirubin nomogram [Clin Perinatol, 25:33, 1998] at any time during the first 168h of life. The ETCOc was determined by the CO-Stat™ End Tidal Breath Analyzer (Natus Medical Inc., San Carlos, CA). Of the 564 subjects who successfully completed the protocol, 47 (8.3%) were determined to be hyperbilirubinemic. The average ETCOc for the hyperbilirubinemic group was significantly higher (38%) than the non-hyperbilirubinemic group (p < 0.0001). Thirty-seven subjects (79%) determined to be hyperbilirubinemic had ETCOc measurements higher than the mean of the non-hyperbilirubinemic group. An ETCOc > 75th percentile had a 58% positive- and a 95% negative predictive value. An ETCOc > 75th percentile or a STB at 30h > 75th percentile yielded an 87% positive- and 98% negative predictive value. We conclude that elevated bilirubin production is an important contributing factor in the majority of cases of hyperbilirubinemia, but the best prediction of jaundice is achieved by assessing bilirubin production and elimination together.

(Supported by a grant from Natus Medical, Inc.)