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Analysis of federal survey data indicated that testosterone levels in boys versus girls had almost fully diverged by age 12, with no overlap between interquartile ranges.

The study by Jonathon Senefeld, PhD, of the Mayo Clinic in Rochester, Minnesota, and colleagues published in a helps clarify the testosterone trajectory during adolescence.

Pinpointing when testosterone levels diverge between male and female youths is clinically beneficial for a few reasons, Senefeld's group explained. For example, it could be useful when evaluating youths for pubertal and androgenic disorders.

Knowing when testosterone levels diverge between males and females also holds implications for youth competing in sports as "serum testosterone has been demonstrated to be strongly associated with sex differences in athletic performance," the researchers noted.

Between the ages of 6 and 10, youths saw similar testosterone levels regardless of sex. At the age of 6, total testosterone concentrations for male and females in the 50th percentile were 1.9 ng/dL and 2.4 ng/dL, respectively (P<0.64).

When youths first started to diverge at age 11, median testosterone concentrations for males in the 50th percentile were 13.3 ng/dL, while females in the 50th percentile saw testosterone levels around 14.2 ng/dL (P<0.001). However, 11-year-old males in the 95th percentile saw median testosterone concentrations as high as 327 ng/dL, while 11-year-old females in the 95th percentile for testosterone concentrations saw levels around 38.5 ng/dL.

This divergence was maintained throughout adulthood. By age 20, females had a median testosterone concentration of 29.5 ng/dL, while males had median testosterone levels of around 516 ng/dL.

Between ages 6 and 20, females saw their testosterone levels plateau by age 14 while males didn't see a plateau in testosterone until age 17.

In discussing the study's implications, Senefeld's group pointed out that "[p]otential testosterone thresholds for eligibility in sports may need to be adjusted based on further information on outliers and direction of error accepted."

Additionally, the data could be helpful for gauging timing of puberty in adolescents who are gender-dysphoric, gender-incongruent, or transgender.

According to , puberty blocking and gender-affirming hormone treatment in prepubertal children with gender dysphoria or gender incongruence is not recommended. However, after girls and boys first begin to exhibit physical changes associated with puberty, clinicians are recommended to begin pubertal hormone suppression.

For the analysis, Senefeld's group drew upon data from the 2013-2014 and the 2015-2016 periods of the National Health and Nutrition Examination Survey. This included testosterone samples on 4,495 youth from the U.S. (2,293 males; 2,202 females). The sample was racially diverse with about 36% Hispanic, 27% white, 23% Black, 9% Asian, and 6% multiracial. There were no significant differences in testosterone between the races.

Study limitations included a lack of information of the pubertal stages of the individuals, as well if any individuals had androgenic disorders. Additionally, sex identification was usually reported by the parent and didn't identify transgender or gender incongruent youths.

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