A study published in The Journal of Urology, an Official Journal of the American Urological Association (AUA), suggests that for men in their mid-forties and younger, the typical threshold for low testosterone levels may not be correct.
“Young men have different testosterone reference ranges than older men,” comments lead author Alex Zhu, DO, of the University of Michigan, Ann Arbor. “Our findings suggest we should be using age-specific cutoffs when assessing testosterone levels in younger men.”
Different thresholds for low testosterone in younger men
Patients suffering from testosterone deficiency have low levels of the male sex hormone testosterone, which causes symptoms such as decreased sex drive and erectile dysfunction. Testosterone deficiency is often thought to be a disease that affects older men. However, younger men with worries about testosterone deficiency are becoming more common, and they often present with less-specific symptoms like fatigue and low energy.
Detecting low testosterone in young males also presents additional difficulties. 300 nanograms per deciliter (ng/dL) is the accepted threshold value for low testosterone. That criterion, however, ignores the normal age-related drop in testosterone levels and is based on testosterone studies of older men.
Dr. Zhu and colleagues from the University of Michigan Department of Urology analyzed data on roughly 1,500 males, aged 20 to 44, from a national health study (the National Health and Nutrition Examination Survey, or NHANES) to create a set of age-specific cutoff points. Men on hormone therapy or with a history of testicular cancer or testicular removal (orchiectomy) were excluded from the study. Because of the normal daily fluctuations in testosterone levels, the research solely used morning testosterone measurements.
The range of testosterone levels was evaluated in five-year age groups. The middle tertile (one-third) of the testosterone level distribution in each five-year age group was defined as the normal range. Values below this range were used to calculate age-specific thresholds for low testosterone levels.
As expected, testosterone levels decreased at older ages. Age-specific cutoff points for low testosterone ranged from 409 ng/dL at age 20 to 24 years to 350 ng/dL at age 40 to 44 years – substantially higher than the standard cutoff point. Each one-year increase in age was associated with a 4.3 ng/dL decrease in testosterone level.
The study provides “the first evaluation of normative, population-based testosterone levels for young men in the United States,” according to the authors. They note that their study reflects the racial/ethnic diversity of the US population, and doesn’t exclude men with health conditions other than testicular cancer or prior orchiectomy.
“In today’s age of personalized medicine, clinicians can now use age-specific testosterone levels to evaluate young men instead of relying on a ‘one size fits all’ approach,” Dr. Zhu and coauthors write. They highlight the need for further studies, including how to interpret age-specific cutoffs in the context of testosterone deficiency symptoms. The researchers also note that the age-specific cutoffs may affect insurance policies – which sometimes do not cover testosterone therapies unless the testosterone level is below the standard 300 ng/dL cutoff.
Reference: “What Is a Normal Testosterone Level for Young Men? Rethinking the 300 ng/dL Cutoff for Testosterone Deficiency in Men 20-44 Years Old” by Alex Zhu, Juan Andino, Stephanie Daignault-Newton, Zoey Chopra, Aruna Sarma and James M. Dupree, 1 December 2022, The Journal of Urology.