Chronobiologic reference values in clinical chemistry.

Circadian rhythms of 23 biochemical parameters were studied in the serum of 194 children 11 +/- 1.5 years of age, 43 young adult subjects 21 +/- 2 years of age and 200 elderly subjects 77 +/- 8 years of age. In the children and the elderly subjects, the investigations extended over all four seasons allowing also the study of seasonal variations or circannual rhythms. The circadian rhythms were characterized by population mean cosinor for each group and sex. The circannual rhythms were explored by single cosinor and one and two way analysis of variance applied to the circadian means obtained during each season, and by the comparison of the circadian rhythm parameters obtained during the four seasons by the parameter test described by Bingham et al. Circadian rhythms were found in most and circannual rhythms in many parameters. The rhythm characteristics are presented as cosinor summaries. A number of laboratory parameters show high amplitude rhythms in one or the other frequency studies and require time-qualified reference ranges for a meaningful use of these variables for clinical diagnosis. The majority shows small amplitude rhythms, which do not pose diagnostic problems, but are indicators of the complex time structure of the human organism.