Circannual rhythms of laboratory measurements in serum of elderly subjects.

A total of 160 elderly subjects 77 +/- 8 years of age were studied in 201 24-hr profiles consisting of six blood samples collected at 4-hr intervals. The sampling sessions were spread over all four seasons. The circadian means were analyzed (one-way ANOVA) for the presence of circannual variations. Statistically significant circannual variations were found in the serum concentrations of albumin, bilirubin, calcium, chloride, CPK, globulin (calculated), glucose, LDH, potassium, sodium, triglycerides, uric acid, and total protein. The data presented indicate that many chemical constituents commonly measured in human serum and urine show seasonal variations in elderly subjects, some of which are large enough to present potential diagnostic problems. Others may not pose diagnostic problems in today's practice of laboratory medicine, but indicate seasonal changes in metabolic functions or, if endogenous in nature, circannual rhythms that 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.