Harvard Men's Health Watch

Testosterone testing is more flexible in older men

Testosterone levels can fluctuate over the course of the day, so medical guidelines recommend that men get blood drawn for hormone tests in the morning, when testosterone is highest. But morning measurements may be less important for older men, according to a study in the Journal of Urology.

Researchers looked at testosterone levels measured in 2,600 men who went to an erectile dysfunction clinic. In men younger than 45, testosterone was highest at 7 a.m. but as much as 33% lower by 2 p.m. In contrast, the levels in older men varied very little.

However, testosterone levels can vary for reasons other than time of day, making it uncertain that a single test result truly reflects the level of biologically active hormone in a man's system. For example, having a chronic illness or being overweight can suppress testosterone levels. Borderline-low test results can be especially hard to interpret.

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