Neonatal bilirubin production-conjugation imbalance: effect of glucose-6-phosphate dehydrogenase deficiency and borderline prematurity.

OBJECTIVE To evaluate relations between production and conjugation of bilirubin in the pathophysiology of jaundice in glucose-6-phosophate dehydrogenase (G6PD) deficient neonates. METHODS Term and borderline premature (35-37 weeks gestational age), healthy, male, G6PD deficient neonates were studied close to the beginning of the 3rd day. Blood carboxyhaemogobin corrected for inspired CO (COHbc; an index of bilirubin production) and serum total conjugated bilirubin (TCB; a reflection of bilirubin conjugation) were measured in simultaneously drawn blood samples by gas chromatography and reverse phase high performance liquid chromatography respectively. A bilirubin production-conjugation index comprising COHbc/TCB was determined; a high index reflects imbalance between the bilirubin production and conjugation processes. COHbc and TCB individually and the production-conjugation index were studied in relation to serum total bilirubin (STB) concentration. RESULTS Fifty one G6PD deficient neonates were sampled at 51 (8) hours. COHbc values did not correlate with STB (r=0.22, p=0.15). TCB did correlate inversely with STB (r=-0.42, p=0.004), and there was a positive correlation between the production-conjugation index and STB (r=0.45, p=0.002). The production-conjugation index (median (interquartile range)) was higher in the premature (n=8) than term neonates (2.31 (2.12-3.08) v 1.05 (0.53-1.81), p=0.003). This difference was the result of changes in TCB. CONCLUSIONS The data show that jaundice in G6PD deficient neonates is the result of an imbalance between production and conjugation of bilirubin with a tendency for inefficient bilirubin conjugation over increased haemolysis in its pathogenesis. Borderline premature infants are at special risk of bilirubin production-conjugation imbalance.