The Effect of Diurnal Variation on Clinical Measurement of Serum Testosterone and Other Sex Hormone Levels in Men

Context: Although diurnal variation of testosterone and other hormones in men has been well documented, the effect of this variation on sampling during typical clinic hours has not been examined. Objective: Our objective was to examine temporal variation in serum testosterone and five other hormones in men over normal clinic hours. Design: Blood samples were collected at six separate visits, three morning visits 1-3 d apart and three afternoon visits 1-3 d apart. Setting and Participants: In Boston, MA, 66 men participated, 30-80 yr of age, randomly selected from the Boston Area Community Health Survey who completed at least five visits. Main Outcome Measures: The age-specific ratio of hormone level at times ranging from 0801-1600 h to hormone level at 0800 h was calculated. Ratios were calculated from parameter estimates obtained from cosinor models. Results: In men 30-40 yr old, testosterone levels were 20-25% lower at 1600 h than at 0800 h. The difference declined with age, with a 10% difference at 70 yr. 17 men with at least one of three measurements less than 300 ng/dl (10.4 nmol/liter) after 1200 h had normal testosterone levels at all three visits before 1200 h (five of eight men 30-47 yr old, four of nine men 66-80 yr old). Much lower levels of diurnal variation were found for dihydrotestosterone, SHBG, LH, FSH, and estradiol at all ages. Conclusions: Our results support the recommendation of restricting testosterone measurements to morning hours in both young and older men. Limited diurnal variation in other hormones indicates that sampling through the day is appropriate. (J Clin Endocrinol Metab 94: 907-913, 2009)