Circadian variability of bilirubin in healthy men during normal sleep and after an acute shift of sleep.

Bilirubin is a laboratory test widely used for patient care, especially neonatal patients and patients with anemia or suspected liver disorders. Bilirubin has also been shown to be associated with sleep pattern and oxidative stress. The aim of this study was to investigate the variation of bilirubin in a group of healthy individuals with normal night sleep as well as during acutely displaced sleep, as sleep timing varies immensely between individuals while clinical samples are still mainly taken in the morning. We studied the diurnal variation of bilirubin during night-sleep and day-sleep conditions in seven healthy volunteers. Serum samples were collected every hour (50 samples/individual) to evaluate the effect of different sampling times and sleep displacement on the test results. The mean acrophases (peak time) occurred at 10.6 h during the night-sleep condition and at 18.4 h during the day-sleep condition. The diurnal intraindividual variation was high during both the night-sleep and day-sleep conditions, with coefficients of variation (CV) in the range of 12.8 to 42.5%. The diurnal variation was higher during the day compared to night-sleep condition. Thus, bilirubin sampling should be restricted to the morning, preferably after a normal night sleep, to minimize intraindividual variation.