The Utility of Serum Free Testosterone Concentrations in Monitoring Gender-Affirming Testosterone Therapy in Transmasculine Youth with Obesity

Jeremi M Carswell; Ellis Barrera; Enju Liu; Stephanie A Roberts

doi:10.1089/trgh.2022.0215

. 2025 Oct 10;10(5):428–437. doi: 10.1089/trgh.2022.0215

The Utility of Serum Free Testosterone Concentrations in Monitoring Gender-Affirming Testosterone Therapy in Transmasculine Youth with Obesity

Jeremi M Carswell ^1,^2,^*, Ellis Barrera ¹, Enju Liu ^2,³, Stephanie A Roberts ^1,²

PMCID: PMC12670710 PMID: 41340815

Abstract

Purpose:

This study aimed to explore the use of serum free testosterone concentrations in transmasculine patients as a more reliable indicator of gender-affirming testosterone therapy than total testosterone concentration. Total testosterone values, recommended by current guidelines, may be impacted by obesity. In addition, this study aimed to characterize the impact of testosterone concentrations on hematocrit and the risk of polycythemia.

Methods:

A retrospective study was conducted of transmasculine patients seen at Boston Children’s Hospital Gender Multispecialty Service from 2007 to 2020. Sixty-eight birth-assigned female adolescents who were receiving gender-affirming testosterone therapy and had total and free testosterone concentrations were included. The aims were to determine the fidelity of total and free testosterone concentrations with body mass index (BMI) and to characterize the association of testosterone concentrations with erythrocytosis.

Results:

Of 68 subjects, 23% were overweight and 40% had obesity. Compared with the group with a healthy BMI, patients with obesity had significantly lower total testosterone concentrations. Free testosterone concentrations did not vary based on BMI category. BMI z-score was inversely correlated with total testosterone, sex hormone-binding globulin, and albumin concentrations but not with free testosterone concentrations. Four percent of subjects developed erythrocytosis (e.g., hematocrit >50%). Neither BMI nor testosterone concentrations were correlated with hematocrit.

Conclusions:

Free testosterone concentrations are an adjunctive tool in the monitoring of gender-affirming testosterone therapy. In addition, the development of erythrocytosis is independent of serum testosterone concentration and warrants further study to understand factors that may predispose patients to developing secondary polycythemia.

Keywords: free testosterone, gender-affirming hormones, gender diverse, testosterone, transgender

Introduction

A dramatically increasing number of transgender and gender diverse (TGD) youth are presenting to pediatric transgender health programs for gender-affirmative care.¹ As awareness surrounding gender-affirming care for adolescents increases, more TGD assigned female at birth (AFAB) individuals are initiating testosterone as part of their medically necessary care.^2–7 Current guidelines include weekly injections of subcutaneous testosterone for gender affirmation, which our program and others have used with clinical success, in TGD youth with gender dysphoria.^8–11

Current clinical practice guidelines recommend the monitoring of total testosterone concentrations to adjust maintenance dosing to mimic physiological testosterone concentrations, concordant with values that would be expected for cisgender peers.^8,9 Measurement of serum total testosterone is recommended every 6–12 months in transgender males undergoing pubertal induction, and every 3 months for older adolescents and adults, until concentrations are in the physiological cisgender male range (e.g., 400–700 ng/dL).^8,9 However, these recommendations do not account for factors that may influence the interpretation of total testosterone concentrations, such as obesity. Some studies have reported a greater proportion of transgender youth as overweight or obese compared with the general population, especially in those AFAB.^12,13 Furthermore, gender-affirming testosterone therapy has been associated with an increase in body mass index (BMI) over time, even when compared with BMI-matched cisgender females.¹³ In addition, rates of obesity have been increasing and been exacerbated by the COVID-19 pandemic.¹⁴

Testosterone, like many hormones, exists in both free and bound forms with the assumption that it is the unbound form that has the most biological activity. The significance of these findings is supported by the assessment of serum testosterone concentration that includes a predominance of testosterone bound to sex hormone-binding globulin ([SHBG]; 60–80%), a small proportion bound to albumin (20–40%), and an even smaller amount circulating as free testosterone (2–3%).¹⁵ Measurement of free testosterone is recommended in the evaluation of suspected hypogonadism in cisgender men with altered SHBG concentrations or when total testosterone concentrations are at the lower end of the normal range for total testosterone.¹⁶ This study aimed to explore the use of serum free testosterone concentrations in transmasculine patients as a more reliable indicator of monitoring gender-affirming testosterone therapy than total testosterone concentration. We hypothesized that patients with overweight and obese BMI, whose total testosterone concentrations were low, would exhibit free testosterone concentrations in the normal range for late pubertal cisgender males. In addition, this study aimed to characterize the impact of testosterone concentration on hematocrit and the risk of polycythemia. We hypothesized that total testosterone concentration would positively correlate with hematocrit.

Materials and Methods

Participants

This was a retrospective chart review of all patients seen at the Boston Children’s Hospital Gender Multispecialty Service between 2007 and 2020. The study was reviewed and approved by the Boston Children’s Hospital Institutional Review Board and determined to be exempt from requiring patient consent given the nature of the study. Subjects were identified by an initial query using the International Classification of Diseases, Ninth Revision (ICD-9) and ICD-10 codes for gender identity disorder/gender dysphoria and a free testosterone concentration utilizing the institution’s Clinical Research Institutional Technology services. Inclusion criteria included an AFAB sex, diagnosis of gender dysphoria, no history of pubertal suppression with gonadotropin-releasing hormone agonist, currently using injected subcutaneous testosterone therapy, and having concurrent total and free testosterone concentrations available. Testosterone concentrations were collected only if anthropometric measurements were also available. For a small subset of subjects with multiple testosterone concentrations available, the first available measurements at least four months after initiation of gender-affirming testosterone therapy were collected.

Exclusion criteria included TGD youth evaluated at Boston Children’s Hospital but not receiving gender-affirming care in our program and AFAB youth with gender dysphoria who were not receiving gender-affirming testosterone therapy. Eligible subjects were determined by chart review, and phenotyping data including demographic information, medications, anthropometric data, and biochemical data (e.g., total and free testosterone concentrations, albumin, SHBG, hematocrit) were collected in a REDCap database. Biochemical data obtained only at Boston Children’s Hospital were included for analysis. Percentile and z-score for weight, height and BMI were determined by the Centers for Disease Control and Prevention’s (CDC) girls’ growth charts.¹⁷ Overweight was defined as a BMI percentile between ≥85th percentile and <95th percentile, and obesity was defined as ≥95th percentile by current clinical standards using the CDC growth chart for BMI-for-age.^17–19

Biochemical assays

Serum laboratory measurements were performed at Boston Children’s Hospital. Total testosterone concentrations were measured by liquid chromatography–mass spectrometry on a Sciex API6500 mass spectrometer with an Aria TLX-2 chromatography system using a C18 column. SHBG concentrations were measured using the Abbott SHBG chemiluminescent microparticle immunoassay on an Architect i1000 instrument. Albumin concentrations were measured using the Roche Diagnostics bromocresol purple colorimetric method on a Roche Cobas c501. Free testosterone concentrations were calculated using the Vermeulen quadratic equation.²⁰ Samples of free testosterone concentrations at Boston Children’s Hospital have been validated against sample sets provided by the CDC; the most recent sample set had 1 sample with a 2% variance, and the other 2 sets were <1% different from the CDC measured value. Bioavailable testosterone concentrations were subsequently calculated as previously described.²⁰

Statistical analysis

All statistical analyses were conducted using SAS software (version 9.4, Cary, NC) and/or GraphPad Prism (10.0.2, La Jolla, CA). The mean and standard deviation (SD) or median and interquartile range (IQR) were used to describe continuous variables and the frequency and percentage to describe categorical variables. Linear regression and Pearson correlation coefficients were used to determine the relationship between two continuous variables. Multiple linear regression models were used to assess the association of outcomes with two or more independent variables simultaneously. Statistical significance was defined as p values <0.05; all tests were two-sided.

Results

Demographics

Our inclusion criteria identified 68 AFAB subjects (Table 1). The median (IQR) age of presentation to our pediatric transgender health program was 16.4 (14.8–17.5) years. A predominance (99%) had a male gender identity and 1% had a non-binary gender identity. This may reflect the study period as there is considerable variability in the percentage of youth reported as non-binary identified.²¹ The majority of subjects were White (94%) with a small percentage identifying as Black or African American (3%) or Asian (3%). The majority (97%) of subjects had Tanner stage V breast development at the time of gender-affirming testosterone initiation and the median (IQR) age of menarche (100%, n = 68) was 11.0 (11.0–12.0) years.

Table 1.

Demographic and Anthropometric Characteristics of Subjects (n = 68)

Age at first visit, median (IQR), y	16.4 (14.8–17.5)
Affirmed gender, n (%)
Transgender male	67 (99%)
Non-binary	1 (1%)
Race, n (%)
White	64 (94%)
Black or African American	2 (3%)
Asian American	2 (3%)
Indian/Alaska Native	0 (0%)
Native Hawaiian/Pacific Islander	0 (0%)
Ethnicity, n (%)
Non-Hispanic	64 (94%)
Hispanic	4 (6%)
Tanner stage, n (%)
II	0 (0%)
III	1 (1.5%)
IV	1 (1.5%)
V	66 (97%)
Age of menarche, median (IQR), y	11.0 (11.0–12.0)
Age of initiation of gender-affirming testosterone therapy, mean (±SD), y	17.0 (±1.6)
Initial dose of weekly SC testosterone cypionate, median (range), mg	26.8 (25–50)
Weight, median (IQR), kg	75.2 (59.7–93.1)
Weight z-score, median (IQR)	1.3 (0.2–2.1)
Height, median (IQR), cm	163.6 (159.0–168.3)
Height z-score, median (IQR)	0.1 (−0.6–0.8)
BMI, median (IQR), kg/m²	27.6 (22.4–36.0)
BMI z-score, median (IQR)	1.3 (0.4–2.1)
BMI categories, n (%)
Underweight	0 (0%)
Healthy weight	25 (37%)
Overweight	16 (23%)
Obese	27 (40%)

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BMI, body mass index; IQR, interquartile range; SC, subcutaneous; SD, standard deviation; y, years.

The mean (±SD) age of gender-affirming hormone initiation was 17.0 (±1.6) years using weekly subcutaneous testosterone cypionate with an initial dose of 25–50 mg. Regular subcutaneous administration of testosterone esters has been shown to be an effective method of providing masculinizing hormones in TGD youth and young adults.^10,11

Anthropometric measurements

The median (IQR) absolute BMI was 27.6 (22.4–36.0) kg/m², and the median (IQR) BMI z-score was 1.3 (0.4–2.1; Table 1). No patients were underweight, 37% were healthy weight, 23% were overweight, and 40% were obese. The use of the BMI-for-age growth chart for girls was utilized, concordant with other studies in TGD youth; however, which gendered growth chart is most appropriate remains unclear given a lack of evidence.²²

Impact of BMI on testosterone concentration

Median (IQR) total and free testosterone concentrations were 428.0 (283.0–557.8) ng/dL and 100.1 (68.3–153.7) pg/mL, respectively (Table 2; including cisgender male reference ranges). One patient had a total testosterone concentration of 1120 ng/dL and free testosterone concentration of 275.1 pg/mL, which were elevated compared to the rest of the cohort, and their dose of testosterone cypionate was decreased from 50 mg to 40 mg subcutaneous weekly. Bioavailable testosterone concentrations, which account for free testosterone plus testosterone weakly bound to albumin, were calculated at a median (IQR) of 237.0 (157.5–342.5) nmol/L.²⁰ Median (IQR) total testosterone concentrations in healthy, overweight, and obese subjects were 545.0 (373.0–750.0) ng/dL, 443.0 (252.3–531.8) ng/dL, and 340.0 (206.0–444.0) ng/dL, respectively. Obese BMI (p < 0.001), but not overweight BMI (p = 0.70), in comparison to healthy weight BMI, was associated with significantly lower total testosterone concentrations. No association was found between free testosterone concentrations and BMI categories (overweight p = 0.69; obese p = 0.11 in comparison to healthy weight). Median (IQR) SHBG and albumin concentrations were 21.7 (13.9–32.5) nmol/L and 4.6 (4.4–4.8) g/dL, respectively.

Table 2.

Serum Hormone Concentrations of Patients on Gender-Affirming Testosterone Therapy

	Total (n = 68)	Healthy Weight (n = 25)	Overweight (n = 16)	Obese (n = 27)
Total testosterone, median (IQR), ng/dL [400.0–1000.0]^a	428.0 (283.0–557.8)^*	545.0 (373.0–750.0)	443.0 (252.3–531.8)	340.0 (206.0–444.0)
Free testosterone, median (IQR), pg/mL [41.0–239.0]	100.1 (68.3–153.7)	122.3 (70.5–184.9)	91.5 (68.3–123.2)	98.7 (63.7–127.1)
Bioavailable testosterone, median (IQR), nmol/L	237.0 (157.5–342.5)	285.0 (162.5–433.0)	216.0 (166.0–296.0)	206.0 (154.0–293.0)
Sex hormone-binding globulin, median (IQR), nmol/L [11.1–71.0]	21.7 (13.9–32.5)^*	31.7 (20.0–36.5)	25.2 (18.2–35.0)	16.6 (11.0–20.5)
Albumin, median (IQR), g/dL [3.0–4.6]	4.6 (4.4–4.8)^*	4.7 (4.5–4.8)	4.6 (4.5–4.8)	4.5 (4.3–4.8)
Hematocrit, median (IQR), % [33.0–43.4]	45.1 (42.4–47.1)	44.4 (41.7–46.8)	43.6 (40.7–45.3)	46.6 (44.6–48.9)

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^{^a}

Normal range for cisgender males denoted in brackets for measured variables. Tanner stage V male standards utilized for total and free testosterone and sex hormone-binding globulin concentrations.

^{^*}

p < 0.05 for association between body mass index and biochemical parameter.

g/dL; gram/deciliter; nmol/L; nanomole/liter; ng/dL, nanogram/deciliter; pg/mL; picogram/milliliter.

Total testosterone concentrations were significantly decreased with increasing BMI z-score (Fig. 1A; r = −0.35, p < 0.05) but not in association with free testosterone (Fig. 1B; r = −0.13, p = 0.37) nor bioavailable testosterone concentrations (Fig. 1C; r = −0.17, p = 0.25). SHBG (Fig. 2A; r = −0.44, p < 0.01) and albumin (Fig. 2B; r = −0.42, p < 0.01) had a significantly inverse relationship with BMI z-score.

FIG. 2. — Relationship of body mass index on testosterone-binding proteins and hematocrit. SHBG (A; r = −0.44, p < 0.01) and albumin (B; r = −0.42, p < 0.01) were significantly inversely correlated with BMI z-score. There was not a significant relationship with hematocrit and BMI z-score (C; r = −0.19, p = 0.22). BMI z-score determined by the Centers for Disease Control and Prevention BMI-for-age chart for girls. SHBG, sex hormone-binding globulin.

Effects of BMI and testosterone therapy on hematocrit

Hematocrit is expected to increase in response to exogenous testosterone therapy, with a goal of maintaining testosterone concentrations within the normal range for cisgender males.^8,9 Median (IQR) hematocrit was 45.1% (42.4–47.1), and 3 patients (4.4%) met the criteria for erythrocytosis as defined by hematocrit >50% (Table 2).⁸ Hematocrit did not have a significant linear relationship with BMI z-score (Fig. 2C; r = 0.19, p = 0.22). Interestingly, hematocrit did not exhibit a significant relationship with total (Fig. 3A, r = 0.01; p = 0.96) nor free (Fig. 3B, r = 0.14; p = 0.29) testosterone concentrations.

FIG. 3. — Percent hematocrit in association with testosterone concentrations. Hematocrit did not exhibit a significant correlation with total (A; r = 0.01; p = 0.96) or free (B; r = 0.14; p = 0.29) testosterone concentrations.

Discussion

Our study aims to advance clinical practice by individualizing the biochemical response to gender-affirming testosterone therapy by avoiding unnecessary upward titrations in dosing and potential complications such as dyslipidemia. Changes in the lipid profile in response to testosterone therapy are expected, and transmasculine patients with obesity have been documented to have a greater reduction in high-density lipoprotein cholesterol compared to youth without obesity.^23,24 In addition, individualized medicine is important as TGD youth report significantly poorer overall health, lower rates of preventative health visits, and more nurse office visits compared with cisgender peers.⁸

Free testosterone concentrations have been reported in transmasculine youth receiving testosterone therapy, however have not been widely utilized as a strategy to alter clinical management.^10,11,23 Spratt et al. reported one adult transgender male with a lower total testosterone concentration on weekly subcutaneous therapy with a normal free testosterone concentration.²⁵ In their cohort of 63 transmasculine adults, they reported no impact of BMI on the dose of subcutaneous testosterone nor serum total testosterone concentration. However, the authors note that there was a statistically significant difference in total testosterone concentrations between healthy weight and obese groups.²⁵ Current guidelines do not advise on the use of bioavailable nor free testosterone concentrations in the monitoring of youth on gender-affirming testosterone therapy.^8,9

Measurement of free testosterone concentrations is recommended in the evaluation of suspected hypogonadism in cisgender men with altered SHBG concentrations or when total testosterone concentrations are at the lower end of the normal range.¹⁶ Free testosterone concentrations are advised to be assessed directly by equilibrium dialysis assays or calculated from total testosterone, SHBG, and albumin concentrations.¹⁶ Obesity is associated with decreased SHBG concentrations, and androgens such as testosterone also lower SHBG as well.²⁶ As a case in point, calculated free testosterone concentrations are commonly employed in AFAB individuals with polycystic ovarian syndrome (PCOS).²⁷ Our cohort had a predominance of youth with obesity and a statistically significant relationship was found between total testosterone and BMI z-score. BMI z-score was also inversely correlated with SHBG and albumin, which has previously been described.²⁸

Childhood obesity rates are increasing, and transgender youth have been reported to have higher rates of obesity, compared with the general population, in some cohorts.^12–14 Our findings suggest that the free testosterone concentrations in transmasculine adolescents with obesity may be a more accurate indicator of biochemical response to exogenous testosterone therapy. Total testosterone concentrations were significantly decreased with greater BMI z-score, but free and bioavailable testosterone concentrations were not affected. Absolute BMI was also significantly associated with a reduction in total testosterone concentrations. When assessed as a categorical variable, an obese BMI was statistically associated with a lower total testosterone concentration in obese patients, suggesting this should be considered in transmasculine patients with a BMI ≥95th percentile.¹⁹

Erythrocytosis in response to testosterone therapy is characterized by an elevated red blood cell mass due to secretion of erythropoietin and/or reduced ferritin and hepcidin concentrations.²⁹ Testosterone use in transgender males is associated with a ‘very high risk’ of adverse outcomes in association with erythrocytosis (hematocrit >50%) by current clinical practice guidelines.⁸ Current guidelines recommend measuring hematocrit or hemoglobin every three months during the first year and once or twice yearly subsequently.^8,9 Our study did not find an association between hematocrit and BMI z-score. Interestingly, greater concentrations of total or free testosterone concentrations were not correlated with increased hematocrit, suggesting other factors, such as hereditability, may contribute to individual risk of developing polycythemia. Obesity may also be implicated in secondary polycythemia in the setting of obstructive sleep apnea or obesity hypoventilation syndrome.³⁰

In our cohort, 3 (4.4%) individuals developed polycythemia. Mullins et al. have previously reported in their cohort of 504 transgender youth that 2% developed erythrocytosis.³¹ In another cohort of 119 transmasculine youth described by Laurenzano et al., none were reported to develop polycythemia in response to subcutaneous testosterone therapy.¹¹ A recent publication in 1073 adult transgender men followed for 20 years longitudinally, reported the occurrence of erythrocytosis was most likely to occur on the first year of therapy; however, it still occurred with ongoing duration of therapy (e.g., 38% after 10 years).³² A study of 180 adult transgender men had no difference in mean total testosterone concentrations; however, a higher proportion of patients with intramuscular testosterone developed erythrocytosis compared with transdermal testosterone.³³

Limitations

There are several limitations to our study. As data were extracted through retrospective chart review, we could not comment on the efficacy of testosterone action or patient satisfaction. Additionally, these were not the stated aims of this study. In addition, serum testosterone concentrations, instead of testosterone dosing, were examined to account for individual biochemical responses to therapy. Given the retrospective nature of the study design, there may have been variability in when labs were drawn relative to an exogenous testosterone injection; in our clinical practice, peak concentrations are recommended. However, relatively stable serum total and free testosterone concentrations, using weekly subcutaneous testosterone injections have been previously reported.³⁴ Laurenzano et al. found no difference in mean serum testosterone concentrations based on whether obtained as peak or trough values; therefore, the exact timing is unlikely to influence our results.¹¹ The duration of treatment and dose could not be accounted for in the analysis given the size of the cohort; however, there was a relatively narrow dosing range.

Our study was unable to accurately assess other factors that could influence SHBG concentrations in adolescents including insulin resistance, type 2 diabetes, hypothyroidism, acromegaly, and other androgens, such as danazol or oxandrolone, although the latter medications are not currently prescribed in our program.^35,36 There were an insufficient number of baseline total and free testosterone concentrations (e.g., obtained prior to gender-affirming hormones) to report to understand if these were normal prior to gender-affirming hormone therapy; however, these have been reported to be generally normal by other investigators.^10,11,23,37

In addition, free testosterone concentrations were not assessed by the gold standard, equilibrium dialysis methods; however, these methods may be impractical in standard clinical practice.³⁸ We cannot accurately assess if patients met diagnostic criteria for PCOS, which could influence free testosterone concentrations, which have been reported in some transmasculine youth.^37,39 Finally, there may be some limitations in generalizability as our cohort was predominantly White, reflective of referrals to our pediatrics transgender health program, and has been observed in other cohorts.³⁷

Conclusion

We have shown that calculated free testosterone concentrations may be a more accurate assessment of biochemical response to gender-affirming testosterone therapy than total testosterone concentrations alone in youth with obesity. Bioavailable testosterone, a calculated value derived from free testosterone plus albumin-bound testosterone, does not appear to confer an advantage over the assessment of free testosterone concentrations and is not widely used in practice.⁴⁰ Current clinical practice guidelines suggest increasing the dose of gender-affirming testosterone therapy to achieve the goal of total testosterone concentration. However, our findings suggest that youth with obesity may be best assessed by free testosterone concentrations to avoid unnecessary increases in their dosing.

Acknowledgment

The authors would like to acknowledge their TGD patients and their families for the privilege of participating in their care.

Abbreviations Used

AFAB: Assigned female at birth
BMI: Body mass index
CDC: Centers for Disease Control and Prevention
IQR: Interquartile range
NICHD: Eunice Kennedy Shriver National Institute of Child Health and Human Development
PCOS: Polycystic ovarian syndrome
SD: Standard deviation
SHBG: Sex hormone-binding globulin
TGD: Transgender and gender diverse

Authors’ Contributions

J.M.C.: Conceptualization, methodology, writing—original draft, and supervision. E.B.: Formal analysis, investigation, curation, and visualization. E.L.: Methodology, software, resources visualization, writing—review, and editing. S.A.R.: Conceptualization, methodology, writing—original draft, visualization, supervision.

Author Disclosure Statement

The authors do not have any financial relationships to disclose.

Funding Information

This work was supported by the National Institutes of Health K08HD100595 (NICHD) and the Loan Repayment Program (S.A.R.).

Cite this article as: Carswell JM, Barrera E, Liu E, Roberts SA (2025) The utility of serum free testosterone concentrations in monitoring gender-affirming testosterone therapy in transmasculine youth with obesity, Transgender Health 10:5, 428–437, DOI: 10.1089/trgh.2022.0215.

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26. Kupelian V, Page ST, Araujo AB, et al. Low sex hormone-binding globulin, total testosterone, and symptomatic androgen deficiency are associated with development of the metabolic syndrome in nonobese men. J Clin Endocrinol Metab 2006;91(3):843–850; doi: 10.1210/jc.2005-1326 [DOI] [PubMed] [Google Scholar]
27. Bui HN, Sluss PM, Hayes FJ, et al. Testosterone, free testosterone, and free androgen index in women: Reference intervals, biological variation, and diagnostic value in polycystic ovary syndrome. Clinica Chimica Acta 2015;450:227–232; doi: 10.1016/j.cca.2015.08.019 [DOI] [PubMed] [Google Scholar]
28. Mosli RH, Mosli HH. Obesity and morbid obesity associated with higher odds of hypoalbuminemia in adults without liver disease or renal failure. Diabetes Metab Syndr Obes 2017;10:467–472; doi: 10.2147/DMSO.S149832 [DOI] [PMC free article] [PubMed] [Google Scholar]
29. Bachman E, Travison TG, Basaria S, et al. Testosterone induces erythrocytosis via increased erythropoietin and suppressed hepcidin: Evidence for a new erythropoietin/hemoglobin set point. J Gerontol A Biol Sci Med Sci 2014;69(6):725–735; doi: 10.1093/gerona/glt154 [DOI] [PMC free article] [PubMed] [Google Scholar]
30. Haider MZ, Anwer F. Secondary Polycythemia. StatPearls Publishing: Treasure Island (FL); 2022. [PubMed] [Google Scholar]
31. Mullins ES, Geer R, Metcalf M, et al. Thrombosis risk in transgender adolescents receiving gender-affirming hormone therapy. Pediatrics 2021;147(4):e2020023549; doi: 10.1542/peds.2020-023549 [DOI] [PubMed] [Google Scholar]
32. Madsen MC, van Dijk D, Wiepjes CM, et al. Erythrocytosis in a large cohort of trans men using testosterone: A long-term follow-up study on prevalence, determinants, and exposure years. J Clin Endocrinol Metab 2021;106(6):1710–1717; doi: 10.1210/clinem/dgab089 [DOI] [PMC free article] [PubMed] [Google Scholar]
33. Nolan BJ, Leemaqz SY, Ooi O, et al. Prevalence of polycythaemia with different formulations of testosterone therapy in transmasculine individuals. Intern Med J 2021;51(6):873–878; doi: 10.1111/imj.14839 [DOI] [PubMed] [Google Scholar]
34. McFarland J, Craig W, Clarke NJ, et al. Serum testosterone concentrations remain stable between injections in patients receiving subcutaneous testosterone. J Endocr Soc 2017;1(8):1095–1103; doi: 10.1210/js.2017-00148 [DOI] [PMC free article] [PubMed] [Google Scholar]
35. Key TJ, Allen NE, Verkasalo PK, et al. Energy balance and cancer: The role of sex hormones. Proc Nutr Soc 2001;60(1):81–89; doi: 10.1079/PNS200068 [DOI] [PubMed] [Google Scholar]
36. Grimstad FW, Knoll MM, Jacobson JD. Oxandrolone use in trans-masculine youth appears to increase adult height: Preliminary evidence. LGBT Health 2021;8(4):300–306; doi: 10.1089/lgbt.2020.0355 [DOI] [PubMed] [Google Scholar]
37. Millington K, Schulmeister C, Finlayson C, et al. Physiological and metabolic characteristics of a cohort of transgender and gender-diverse youth in the United States. J Adolesc Health 2020;67(3):376–383; doi: 10.1016/j.jadohealth.2020.03.028 [DOI] [PMC free article] [PubMed] [Google Scholar]
38. Keevil BG, Adaway J. Assessment of free testosterone concentration. J Steroid Biochem Mol Biol 2019;190:207–211; doi: 10.1016/j.jsbmb.2019.04.008 [DOI] [PubMed] [Google Scholar]
39. Mueller A, Gooren LJ, Naton-Schötz S, et al. Prevalence of polycystic ovary syndrome and hyperandrogenemia in female-to-male transsexuals. J Clin Endocrinol Metab 2008;93(4):1408–1411; doi: 10.1210/jc.2007-2808 [DOI] [PubMed] [Google Scholar]
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[B39] 39. Mueller A, Gooren LJ, Naton-Schötz S, et al. Prevalence of polycystic ovary syndrome and hyperandrogenemia in female-to-male transsexuals. J Clin Endocrinol Metab 2008;93(4):1408–1411; doi: 10.1210/jc.2007-2808 [DOI] [PubMed] [Google Scholar]

[B40] 40. Matsumoto AM, Bremner WJ. Serum testosterone assays—accuracy matters. J Clin Endocrinol Metab 2004;89(2):520–524; doi: 10.1210/jc.2003-032175 [DOI] [PubMed] [Google Scholar]

PERMALINK

The Utility of Serum Free Testosterone Concentrations in Monitoring Gender-Affirming Testosterone Therapy in Transmasculine Youth with Obesity

Jeremi M Carswell

Ellis Barrera

Enju Liu

Stephanie A Roberts