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BACKGROUND Hormonal changes influence the composition of vaginal flora, which is directly related to the health of an individual. Transgender men prescribed testosterone experience a vaginal hormone composition that differs from cisgender women. To the author's knowledge, there are no clinical studies evaluating the influence that testosterone administration has on the vaginal microbiome. METHODS Vaginal swabs were self-collected by a cohort of self-identified healthy transgender men prescribed testosterone for at least 1 year (n = 28) and from cisgender women who were used as the comparator (n = 8). Participants completed a questionnaire to indicate the mode and dose of testosterone administration, sexual history, and vaginal health. Serum was collected for hormone analysis. Bacterial community profiles were assessed with broad-range PCR primers targeting the V3–V4 hypervariable region of the 16S bacterial rRNA, next-generation sequencing, and analysis by phylogenetic placement. RESULTS Compared to cisgender women, the vaginal floras of transgender men were less likely to have Lactobacillus as their primary genus. Intravaginal estrogen administration was positively associated with the presence of Lactobacillus in transgender men (P = 0.045). Transgender men had a significantly increased relative abundance of >30 species and a significantly higher α diversity (P = 0.0003). The presence of Lactobacillus was significantly associated with a lower α diversity index (P = 0.017). CONCLUSIONS The vaginal microbiome of transgender men who were assigned a female sex at birth and use testosterone may differ from that of cisgender women. Intravaginal estrogen administration may reduce these differences by promoting colonization with Lactobacillus species and decreasing α diversity.

Background Transgender women and nonbinary people seeking feminizing therapy are often prescribed estrogen as a gender-affirming hormone, which will alter their reproductive hormone axis. Testosterone, estradiol, and other reproductive hormones are commonly evaluated to assess therapy, but reference intervals specific to transgender women have not been established. The objective of this study was to derive reference intervals for commonly measured analytes related to reproductive endocrinology in a cohort of healthy gender nonconforming individuals on stable feminizing hormone therapy. Methods Healthy transgender individuals who had been prescribed estrogen (n = 93) for at least a year were recruited from internal medicine and primary care clinics that specialize in transgender medical care. Total testosterone and estradiol were measured using immunoassay and mass spectrometry; LH, FSH, sex hormone binding globulin, prolactin, progesterone, anti-mullerian hormone (AMH), and dehydroepiandrosterone sulfate (DHEAS) were measured using immunoassay; free testosterone was calculated. Reference intervals (central 95%) were calculated according to Clinical Laboratory Standards Institute guidelines. Results The distribution of results for transgender women was different than what would be expected from cisgender men or women across all measurements. Use of spironolactone was associated with changes in the result distribution of AMH, FSH, LH, and progesterone. Compared to liquid chromatography coupled to tandem mass spectrometry (LC/MS/MS), immunoassay was sufficient for the majority of estradiol and total testosterone measurements; free testosterone added little clinical value beyond total testosterone. Conclusion Reference intervals specific to transgender women should be applied when evaluating reproductive endocrine analytes. Spironolactone is a significant variable for result interpretation of some tests.

Background Gender-affirming therapy with testosterone is commonly prescribed to aid in the masculinization of transgender men. Sex-hormone concentrations are routinely measured, but interpretation of results can be difficult due to the lack of published reference intervals. Methods Healthy transgender individuals who had been prescribed testosterone (n = 82) for at least a year were recruited from internal medicine and primary care clinics that specialize in transgender medical care. Total testosterone and estradiol were measured using immunoassay and mass spectrometry; LH, FSH, SHBG, prolactin, progesterone, anti-Müllerian hormone (AMH), and dehydroepiandrosterone sulfate (DHEAS) were measured using immunoassay; free testosterone was calculated. Reference intervals (central 95%) were calculated according to Clinical Laboratory Standards Institute guidelines. Results When evaluating general endocrine laboratory tests in people using masculinizing hormones, reference intervals for cisgender men can be applied for total and free testosterone and SHBG and reference intervals for cisgender women can be applied for prolactin. Reference intervals for estradiol, LH, FSH, AMH, and DHEAS differ from those used for cisgender men and cisgender women, and therefore should be interpreted using intervals specific to the transmasculine population. For testosterone and estradiol, results from immunoassays were clinically equivalent to mass spectrometry. Conclusion Masculinizing hormones will alter the concentrations of commonly evaluated endocrine hormones. Providers and laboratories should use appropriate reference intervals to interpret the results of these tests.

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