New data on reference ranges for transgender men

Charna Albert

February 2021—Cisgender male reference intervals can be used to interpret testosterone concentrations in transgender and nonbinary adults on masculinizing therapy, but reference intervals specific to the transmasculine population should be used to evaluate estradiol, say the authors of a recently published study (Greene DN, et al. J Appl Lab Med. 2021;6[1]:41–50).

Participants in the study were 82 healthy transgender adults who had been prescribed testosterone for at least one year. The purpose of the study was to derive reference intervals for common endocrine laboratory measurements in adults on masculinizing gender-affirming hormone therapy. In addition to estradiol and free and total testosterone, the researchers measured LH, FSH, SHBG, prolactin, progesterone, AMH, and DHEAS. For estradiol, they derived a reference interval (by LC/MS/MS) with an upper limit of 168 pg/mL.

Most of the endocrine markers the researchers analyzed are not measured routinely in the transgender population, says Dina N. Greene, PhD, DABCC, clinical associate professor, University of Washington Department of Laboratory Medicine. “The gonadotropins are measured in fertility workups, unexplained amenorrhea, or other types of abnormalities that warrant an endocrine workup, whereas being trans doesn’t warrant a complete endocrine workup in and of itself, contrary to popular belief,” Dr. Greene says. But for total testosterone and estradiol, which are routinely monitored, the study gives “a pretty distinct recommendation.”

Testosterone and estradiol are almost always evaluated before and after gender-affirming therapy is initiated, even if threshold concentrations are derived empirically, the authors write. In patients on masculinizing therapy, estradiol is commonly evaluated until cessation of menstruation and may continue to be measured thereafter, Dr. Greene says, “either because of curiosity or continued spot bleeding or because there is continued attenuation related to gender or hormones.”

Using the cisgender male reference interval for estradiol of less than 45 pg/mL, approximately 18 percent of the cohort would have been flagged abnormally high, the authors write. Thus, study results show that “if you use cisgender male reference intervals to interpret estrogen concentrations in transgender men, you are setting unrealistic expectations,” Dr. Greene says. And estradiol intervals for cisgender women are based on the menstrual cycle and “fluctuate wildly depending on the phase, so it’s hard to compare estradiol concentrations in a trans guy on T to [those of] a cisgender woman.” For estradiol, she says, “trans men need their own reference intervals.”

“There’s a consistent group, maybe it’s a quarter, that you never get down to the cisgender male range for estradiol,” says study coauthor Matthew D. Krasowski, MD, PhD, vice chair, clinical pathology and laboratory services, and clinical professor of pathology, University of Iowa Hospitals and Clinics. Dr. Krasowski shared details from the study during a CAP20 virtual session and in an interview with CAP TODAY. “There have been attempts to use estrogen blockers, but the literature on that doesn’t seem promising, and now you’re adding another drug that may have side effects.” Then, too, hormone therapy isn’t necessarily covered by insurance. “So the more complicated you make the treatment regimen, they may not be able to afford it.”

In transgender adults on masculinizing therapy, it is standard of care to measure testosterone every three months for the first year of therapy and at least annually thereafter. Study results contradict the Endocrine Society clinical practice guideline for the treatment of gender-dysphoric persons, which says a goal of masculinizing therapy should be to titrate testosterone concentrations to a range of 400 –700 ng/mL (Hembree WC, et al. J Clin Endocrinol Metab. 2017;102[11]:3869–3903). Dr. Greene and her collaborators contend there is only empirical evidence to support the recommendation. It was arrived at by experts in clinical care, she says, “who are not the experts in setting reference limits that are broadly used by populations. That’s where the clinical lab comes in.” Study results do align with guideline recommendations to use the age-matched cisgender male reference intervals for testosterone.

“In talking to providers who manage these patients,” Dr. Krasowski says, “they’re not usually targeting specific concentrations. They are looking for effects that are gender affirming. Some patients clearly reach that below this range,” while others reach it at higher levels. “If this was your narrow range, it could be frustrating.”

In fact, Dr. Greene says, the suggested testosterone range “doesn’t parallel the ranges we use for cisgender men,” which have a higher upper reference limit. “And oftentimes we don’t set an upper reference limit for cisgender men; it’s just ‘greater than’ whatever the lower limit is.” Putting forth a suggested range is unrealistic because it’s difficult for patients to time their blood draw appointments relative to their most recent dose of testosterone, she says. “If someone has given themselves their weekly or bimonthly dose of testosterone that morning, their concentrations are going to be different than three days later, than a week later.”

In general, the reason testosterone is measured is to help transgender men build a relationship with their gender and new sense of self, she says. Only in limited situations would it be monitored because concentrations are too high or low. “When you’re working with the trans community, there are psychosocial factors you’re trying to attenuate as well as attenuating hormones. So we have this measurement to show these guys, ‘Look, physiologically you’re looking like a man.’ Whatever your definition of that is.”

Dr. Greene has built specific tests that are identified as “testosterone for people on masculinizing hormones” or “testosterone for people on feminizing hormones.”

“That at least allows the proper reference intervals to be appended,” though it places the burden on providers to order the correct test, she says. At the University of Iowa Hospitals, Dr. Krasowski says, if patients have self-identified in the medical record as having a gender identity that is different than their legal sex, “we’re currently suppressing reference ranges that are male- or female-specific. And we have a comment that indicates ‘this may be affected by therapy.’”

“Ideally,” Dr. Greene says, “we would have algorithms that incorporate gender and hormone use in order to append a reference interval that fits a specific population, but far and wide we are bad at that in the laboratory. We have strict binary systems for many things.”

“Our systems are rigid,” she adds, “but our interpretations don’t have to be.”

Other findings from the study show that cisgender male reference intervals can be used to evaluate SHBG in transgender men, and intervals for cisgender women can be used to interpret prolactin. For FSH, LH, progesterone, AMH, and DHEAS, the authors derived reference intervals that differ from those of cisgender men and women.

Progesterone, LH, and FSH are not monitored routinely in transgender people, but they may be evaluated as part of a fertility workup or for specific endocrine conditions. According to the study, the intervals derived for these analytes most closely resemble the follicular phase in cisgender women, with a higher upper reference limit compared with cisgender men but a lower upper limit compared with the ovulatory phase of cisgender women. These analytes may not be interpreted correctly if cisgender male or female reference intervals are applied, but because they are likely to be evaluated case by case and by endocrine or reproductive specialists rather than general practitioners, the authors do not believe that laboratories will need to implement measures to address these ranges. “It would be useful just to include the information,” Dr. Krasowski says.

“These labs don’t exist in a silo,” Dr. Greene says of the tests. “You’re not looking at a progesterone concentration without a clinical picture,” or a complete hormone analysis. An isolated, slightly elevated progesterone in a transgender male patient would not concern her, she says, if everything else looked normal and the patient was satisfied with the results of therapy. But if a transmasculine patient was attempting to conceive and had recently stopped taking testosterone and had a low progesterone, she says, “I would look at that carefully as a trend over time and at what all the hormones are doing together.”

AMH, a marker of ovarian reserve, also is not typically measured in transgender people but may be evaluated in transmasculine patients who wish to conceive. Participants had a slightly higher upper reference limit relative to cisgender women—“an unexpected result,” the authors write, given that one of the treatment goals of masculinizing therapy is amenorrhea.

“We scratched our heads at this one,” Dr. Krasowski says, speculating that results may have differed with a larger or more age-diverse cohort. (The median age was 27.) In addition, no participants were on treatment regimens that included modalities other than testosterone—notable, he says, because in a prior study that found significant decreases in AMH, participants were receiving an aromatase inhibitor and a GnRH agonist in addition to testosterone (Caanen MR, et al. Fertil Steril. 2015;103[5]:1340–1345).