PURPOSE: We investigated whether there are independent intradaily changes in bilirubin levels in normal neonates. METHODS: During the period of January 1996 till July 1996, 100 healthy newborn infants were studied for at least 3 consecutive days. Starting from the third day of life, consistent intradaily changes of bilirubin concentration were observed. And obstetric history, birth history, weight change at 3 days were recorded from chart review. A complete blood cell count was obtained from each subject at the beginning of the study. RESULTS: The mean bilirubin concentrations at morning were 10.4 +/- 1.8mg/dl (3rd day), 11.6 +/- 2.1mg/dl (4th day) and 11.2 +/- 2.7mg/dl (5th day). The mean bilirubin concentrations at evening were 11.1 +/- 2.1mg/dl (3rd day), 11.3 +/- 2.2mg/dl (4th day) and 10.8 +/- 2.8mg/dl (5th day). Interdaily changes of bilirubin levels were found: morning levels were higher compared with those of the evening. CONCLUSION: We showed a consistent diurnal rhythm in bilirubin levels, with higher levels in the morning than in the evening. This diurnal rhythm in serum bilirubin concentration affects endogenous factors as well as exogenous. Mechanism of diurnal variation was unknown.
Bilirubin* ; Blood Cell Count ; Circadian Rhythm ; Humans ; Hyperbilirubinemia, Neonatal ; Infant, Newborn* ; Reproductive History