Seasonal And Biological Variation Of Blood Concentrations Of Total Cholesterol, Dehydroepiandrosterone Sulfate, Hemoglobin A(Ic), Iga, Prolactin, And Free Testosterone In Healthy Women

Background: Concentrations of physiological response variables fluctuate over time. The present study describes within-day and seasonal fluctuations for total cholesterol, dehydroepiandrosterone sulfate (DHEA-S), hemoglobin A(1c) (HbA(1c)), IgA, prolactin, and free testosterone in blood, and estimates within- (CVi) and between-subject (CVg) CVs for healthy women. In addition, the index of individuality, prediction intervals, and power calculations were derived.Methods: A total of 21 healthy female subjects participated in the study. Using a random effects analysis of variance, we estimated CVg and total within-subject variation (CVti), i.e., the combined within-subject and analytical variation,from logarithmically transformed data. Analytical variation was subtracted from CVti to give CVi. CVi was estimated from samples taken monthly during 1 year (CViy), weekly during 1 month (CVim), and six times within 1 day (CVid).Results: A cyclic seasonal variation was demonstrated for total cholesterol, DHEA-S, HbA(1c) prolactin, and free testosterone. Within-day variation was shown for prolactin and free testosterone. The overall mean values for the group and the variability (CViy and CVg) were: 5.1 mmol/L, 5.5%, and 5.0% for total cholesterol; 6.6 mu mol/L, 7.1%, and 21% for DHEA-S; 4.3%, 2.6%, and 3.3% for HbA(1c)/hemoglobin(total); 2.1 g/L, 5.9%, and 13% for IgA; 136 mIU/L, 23%, and 27% for prolactin; and 5.4 pmol/L, 21%, and 29% for free testosterone.Conclusions: Collecting samples at specific hours of the day or times of the year may reduce high biological variation. Alternatively, the number of individuals may be increased and a paired study design chosen to obtain adequate statistical power. (C) 2000 American Association for Clinical Chemistry.