Abstract 1060 Poster Session IV, Tuesday, 5/4 (poster 363)

Unbound bilirubin (UB) is a more sensitive biochemical predictor of bilirubin encephalopathy (BE) as evaluated by auditory brainstem evoked response (BAER) than either total serum bilirubin (SB) or bilirubin albumin (BA) molar ratio in term infants with hyperbilirubinemia. Little data is available for UB in premature infants. We previously reported BA ratios to be more predictive than SB for BAER changes in premature infants. We hypothesized that UB is a better predictor of BE than BA ratio or SB, as evaluated by BAER in 28 to 32 wks gestational age (GA) infants. 50 subjects were studied. GA was assessed by obstetrical dating criteria or Ballard exam. Data were collected for risk factors associated with hyperbiliruminemia-induced neurotoxicity. SB was analyzed as clinically indicated. Aliquots of the same samples were also analyzed for unbound bilirubin by UB analyzer. Serum albumin was determined at 48-72h of age. Bilateral monoaural BAERs were performed on 5 out of 7 days after birth using 80dB nHL unfiltered click stimuli presented at a repetition rate of 39.9 per sec. BAER waveforms were categorized based on response replicability and peak identification. Wave V latencies were serially analyzed when measurable for individual subjects. Normal BAER progression with time was defined as improvement in waveform category and/or decreased wave V latency. BAERs were defined as abnormal when waveform category worsened and/or latency increased over the study interval. Five infants were excluded due to equivocal data. Peak SB, BA ratio and unbound bilirubin (mean ± SD) for the remaining 45 subjects are presented below. Unbound bilirubin was much more strongly associated with changes in BAER suggesting that unbound bilirubin is much more likely to predict the presence of bilirubin encephalopathy than either serum bilirubin or bilirubin:albumin molar ratio in premature infants. (Table)

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