Purpose: There is an age-related decline in male testosterone production. It is therefore surprising that young men are evaluated for testosterone deficiency with the same cutoff of 300 ng/dL that was developed from samples of older men. Our aim is to describe normative total testosterone levels and age-specific cutoffs for low testosterone levels in men 20 to 44 years old.
Materials and methods: We analyzed the 2011-2016 National Health and Nutrition Examination Surveys, which survey nationally representative samples of United States residents. Men 20 to 44 years old with testosterone levels were included. Men on hormonal medications, with a history of testicular cancer or orchiectomy, and with afternoon/evening laboratory values were excluded. We separated men into 5-year intervals and evaluated the testosterone levels of each age group, and for all men 20 to 44 years old. We used the American Urological Association definition of a "normal testosterone level" (the "middle tertile") to calculate age-specific cutoffs for low testosterone levels.
Results: Our final analytic cohort contained 1,486 men. Age-specific middle tertile levels were 409-558 ng/dL (20-24 years old), 413-575 ng/dL (25-29 years old), 359-498 ng/dL (30-34 years old), 352-478 ng/dL (35-39 years old), and 350-473 ng/dL (40-44 years old). Age-specific cutoffs for low testosterone levels were 409, 413, 359, 352, and 350 ng/dL, respectively.
Conclusions: Diagnosis of testosterone deficiency has traditionally been performed in an age-indiscriminate manner. However, young men have different testosterone reference ranges than older men. Accordingly, age-specific normative values and cutoffs should be integrated into the evaluation of young men presenting with testosterone deficiency.
Keywords: hypogonadism; testosterone.