Researchers have found that, in men aged <45 years, total testosterone levels should be checked as close to 7am as possible, owing to a substantial decline in testosterone levels over the course of the day. However, in this study of 2,569 men with erectile dysfunction, patients aged >45 years could have their blood drawn at any time before 2pm without fear of misleading results, suggesting that the circadian rhythmicity of testosterone levels decreases with age.
References
Welliver, R. C. et al. Validity of midday total testosterone levels in older men with erectile dysfunction. J. Urol. 10.1016/j.juro.2014.01.085
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Timing less important for testosterone draw in older men. Nat Rev Urol 11, 184 (2014). https://doi.org/10.1038/nrurol.2014.47
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DOI: https://doi.org/10.1038/nrurol.2014.47
