Circannual rhythms of laboratory parameters in serum of elderly subjects. Evaluation by cosinor analysis.

A total of 189 elderly subjects 76 +/- 8 years of age were studied in 230 24-hour profiles consisting of six blood samples collected at 4 hour intervals. The sampling sessions were spread over all four seasons. The circadian means were analyzed by single cosinor analysis for the presence of circannual variations. Statistically significant circannual variations were found in men and/or in women in the serum concentrations of: albumin, total bilirubin, calcium, chloride, CPK, glucose, LDH, potassium, sodium, triglycerides, and uric acid. Only in few functions is the extent of the circannual rhythms in the variables presented here large enough to present potential diagnostic problems in today's practice of laboratory medicine. However, the seasonal variations in metabolic functions, or if endogenous in nature, circannual rhythms may be of physiologic and pathobiologic importance. There is a need to quantify certain of these rhythms as a predictable portion of variability in laboratory values, and presumably as an indicator of human health.