Normative ranges of testosterone in young men have been identified on the basis of a nationally representative data in a new study, and these data are expected to provide guidance when evaluating younger individuals presenting with signs and symptoms of potential testosterone deficiency, according to the investigators.
It has long been known that the ranges of normal testosterone differ by age, but the authors of this study contend that this is the first large-scale, population-based analysis conducted in the United States of testosterone levels among in men aged 20-44 years.
“These findings will provide valuable information that clinicians can use in the evaluation and management of young men presenting with concerns about testosterone deficiency,” reported a team of investigators led by Alex Zhu, MD, a urology resident at the University of Michigan, Ann Arbor, in the Journal of Urology.
Outside experts, however, disagree, one saying that the conclusions are “far off and irrational.”
A normative range of testosterone is particularly important for the evaluation of hypogonadism because values vary markedly between individuals and within individuals on repeat measurements over a 24-hour period. At least partially because of this variability, many guidelines, including those issued in by the Endocrine Society and the American Urological Association, recommend testosterone assays only in symptomatic individuals in order to reduce risk of detecting low relative levels that are not clinically relevant.
NHANES data provide norms
The data for this study were drawn from the National Health and Nutrition Examination Surveys (NHANES), which sample representative United States residents. The analytic cohort included 1,486 men stratified in 5-year age intervals (20-24, 25-29, 30-34, 35-39, and 40-44).
Because of the known diurnal variation in endocrine levels, only morning total testosterone levels were considered, for consistency. Individuals at risk of disturbed testosterone levels, such as those on hormonal therapy or with a history of testicular cancer, were excluded. Unlike previous analyses that have limited measurements to nonobese individuals without major comorbidities, no such restrictions were imposed in this analysis, which included a sample balanced by race.
After dividing the testosterone levels collected in the NHANES data by tertiles, the cutoff for reduced testosterone were defined as the lowest tertile for each of the five age groups studied.
Consistent with previous reports that testosterone levels decline with age, the cutoff for low testosterone declined for each increase in 5-year age interval after the age of 29 years.
Specifically, these cutoffs were, in order of advancing age, 409 ng/dL (middle tertile range, 409-558), 413 ng/dL (range, 413-575), 359 ng/dL (range, 359-498), 352 ng/dL (range, 352-478), and 350 ng/dL (range, 350-473).
As in the AUA guidelines, which define a total testosterone level below 300 ng/dL “as a reasonable cutoff in support of the diagnosis of low testosterone,” these cutoffs were established without correlation with symptoms. In younger men, like older men, testosterone levels must be within a clinical context.
“Per the AUA guidelines, clinician should consider measuring testosterone levels in patients with certain medical conditions or signs or symptoms of testosterone deficiency, such as depression, reduced motivation, infertility, reduced sex drive, and changes in erectile function,” Dr. Zhu said in an interview, adding that it is appropriate to follow the AUA guidelines “regardless of age.”