Lost in Translation: How Binary Medicine Misreads Trans Bodies

Medicine prides itself on precision. Doctors measure, weigh, test, and calculate to a decimal point. Yet at the very heart of modern healthcare lies an outdated binary: male or female. Everything from lab ranges to medication risk calculators demands one of these two boxes.

For trans people, this binary isn’t just frustrating – it can distort care. Sometimes the impact is subtle, hidden in numbers and assumptions.

One of the clearest examples is the calculation of kidney function, measured as estimated glomerular filtration rate (eGFR). This number is derived from creatinine, a breakdown product of muscle. On average, male-bodied people have more muscle than female-bodied people, so the eGFR formula includes a sex correction factor [1].

The result? The same creatinine level can produce two very different eGFR values:

• For me, with a creatinine of ~100 µmol/L, my lab reported:
  • Female formula: ~60 mL/min (borderline kidney impairment)
  • Male formula: ~83 mL/min (healthy function)

Neither of these tells my whole truth. My muscle mass is now much closer to that of a cis woman, but my overall mass is still higher than the female average. My physiology sits somewhere in-between.

In 2023, this binary trap had consequences. I was denied spironolactone, a medication that could have helped in my transition, because the female eGFR flagged me as “unsafe.” I didn’t know enough to challenge it at the time, but looking back, it was an unnecessary denial rooted not in my actual kidney health, but in a formula that couldn’t see me. Luckily I could afford to pay for the more expensive Leuprorelin injections, but many may have been denied blockers completely due to this.

Recently, I discovered something most clinicians don’t even mention: eGFR can be adjusted for body surface area (BSA). The standard calculation assumes everyone has a body size of 1.73 m² — the mythical “average adult.” By adjusting for my actual height and weight, my “female” eGFR rises to ~74 mL/min [2].

That paints a far more accurate picture: my kidneys aren’t failing, they’re stable. This single adjustment – which the National Kidney Foundation’s calculator provides but many labs don’t – shows how fragile the story is when patients are forced into one of two boxes.

It’s worth noting that eGFR didn’t just adjust for sex – until very recently, it also adjusted for race, specifically assigning Black patients higher eGFR values than non-Black patients with the same creatinine [3].

This was based on the assumption that Black people “on average” had more muscle mass. The effect? Kidney disease was systematically underdiagnosed in Black patients, delaying referrals for specialist care or transplant eligibility. After years of pressure, professional bodies in the US and UK removed race adjustments from eGFR equations [4].

Kidney function is only one example. Everywhere you look, medicine bakes sex into the maths:

• Hormone reference ranges: “male” or “female,” with no space for transition or hormone therapy.
• Blood counts: haemoglobin thresholds differ by sex, sometimes leading to over-investigation or missed anaemia.
• Drug dosing: many medications adjust for sex, based on averages, and trans patients are rarely included in trials.
• Clinical calculators: cardiovascular risk, kidney risk, fracture risk – all sex-adjusted, all binary.

Trans bodies don’t map neatly to population averages. Hormones, surgery, muscle distribution, fat, and lived physiology all combine into something uniquely individual. Forcing binary classification erases this nuance.

And here’s where autonomy matters. How “sex” is recorded in your medical file should be your choice. For most of us, it is vital that our affirmed gender is respected and recorded – because in nearly every part of care, that’s what protects us. But there will be moments where a clinician needs nuance: not to reclassify us, but to interpret results with context.

That means recognising that “male” vs “female” cut-offs aren’t the whole story.

This isn’t an unsolvable problem. We already have the tools to do better:

• Respect affirmed gender in records. Patients should not be reclassified against their will.
• Use trends, not single cut-offs. Stable eGFR over years is more important than “male vs female” point estimates.
• Adopt sex-neutral markers. Cystatin C is an excellent alternative for kidney function [5].
• Adjust for body size. Use BSA-corrected eGFR when available.
• Develop trans-inclusive reference ranges. As more data accumulates, we can model better norms.
• Listen to patients. We often spot blind spots in the system long before the algorithms do.

Conclusion

Medicine is supposed to be about you. About treating the patient in front of you, not an abstract average. Yet the rigid binary baked into so many lab formulas misreads trans bodies, often to our detriment.

The answer isn’t to erase gender from records, or to force trans people back into “birth sex.” It’s to hold space for nuance – to let patients retain autonomy over how they are recorded, while clinicians learn to interpret results in context.

All of our bodies deserve better than a checkbox.

References

1. Levey AS, Stevens LA, et al. A New Equation to Estimate Glomerular Filtration Rate. Ann Intern Med. 2009.
2. National Kidney Foundation. eGFR Calculator. https://www.kidney.org/professionals/gfr_calculator
3. Eneanya ND, Yang W, Reese PP. Reconsidering the Consequences of Using Race to Estimate Kidney Function. JAMA. 2019.
4. Inker LA, Eneanya ND, Coresh J, et al. New Creatinine- and Cystatin C–Based Equations to Estimate GFR without Race. N Engl J Med. 2021.
5. KDIGO Clinical Practice Guideline for the Evaluation and Management of Chronic Kidney Disease. Kidney Int Suppl. 2012.