Evidence Note
Evidence summary
- Question
- Your hormone levels are “in range” — what does that actually tell you, and what does it not?
- Overall certainty
- 🟡 Mixed — how to measure these hormones is on firm ground; the target ranges attached to them are not outcome-validated
- Clinical relevance
- High
- Reading time
- 5 minutes
- Companion review
- Available →
You have a blood test, and you’re told your levels are “in range” — or “on target,” or “where we want them.” It sounds like a verdict: dose correct, job done. But “in range” means something narrower, and shakier, than it sounds.
Two things are worth pulling apart, because they get run together constantly. One is how well these hormones can be measured — which is actually pretty good. The other is how well anyone knows what number to aim at — which is not good at all. Most of the confidence in a target number is borrowed, not earned.
What is the question?
When a clinician says your oestradiol or testosterone is “in range,” this note is the short answer to what that does and doesn’t mean — and how to hold the number sensibly. It is the distilled version of the full review, which grades the target ranges in use rather than simply repeating them.
What does the evidence say?
“In range” is a consensus band, not a validated target. The widely used oestradiol window (100–200 pg/mL) and the testosterone thresholds are largely cisgender reference intervals adopted by expert agreement. A 2025 systematic review looked specifically for evidence that hitting that oestradiol range produces better feminising results or fewer harms — and did not find it. So “in range” tells you your level sits inside a conventional band. It does not tell you that band is right for you.
A single total number can mislead. Only a small, unbound fraction is immediately active, and how much is free depends on a carrier protein, SHBG — which the hormones themselves move. Oestrogen raises SHBG; testosterone lowers it. So the same total reading can mean different amounts of active hormone depending on the direction of treatment, and a total can look reassuringly normal while the active fraction is not what the number suggests.
For feminising, testosterone suppression matters more than a higher oestradiol. Once testosterone is well suppressed, pushing oestradiol higher has not been shown to speed or improve feminisation — and, depending on route, formulation, dose and individual risk factors, may add risk. If any level deserves closer attention here, it is usually whether testosterone is well suppressed — not whether oestradiol is pushed higher.
A “free testosterone” result should be calculated, not measured directly. The direct “free T” blood tests are unreliable; the trustworthy figure is calculated from total testosterone, SHBG and albumin. Timing matters too: injectable hormones rise and fall between doses, so when the blood is drawn changes the number.
For safety, the type and route of oestrogen matter more than the exact level. Transdermal oestradiol (patch or gel) carries the lowest observed clot risk; the older synthetic oestrogen ethinylestradiol carries the most and is avoided. On testosterone, the one signal clearly worth watching is the blood count (haematocrit), which can rise.
How strong is the evidence?
Split it in two, because the two halves are not equal. How to measure — the assays, the timing, the SHBG effect — is on firm ground. What number to aim at is not: there are no trials establishing an optimal level of any of these hormones, the guidelines themselves pick different targets, and the flagship oestradiol range is not validated against outcomes. The honest summary is that we know how to measure these hormones far better than we know whether the target ranges attached to them are right.
Where are the uncertainties?
No one has established the “best” level of any of these hormones against real outcomes — and feminisation, bone, mood and long-term safety may not even share a single best level. Whether routinely chasing levels, rather than how you are actually doing, changes anything once your regimen is stable is genuinely unknown.
“In range” tells you your number sits in a conventional band — not that it is the right number for you.
What does this mean for practice?
None of this means monitoring is pointless. Levels are genuinely useful for checking a medicine is being absorbed, catching an unexpectedly high or low result, and watching real safety signals like the blood count. What it means is to hold the number more lightly: ask what a given test is for, don’t assume “in range” means “optimal,” and expect the level to be weighed against how you actually feel and look — along with the route, the timing, and the free fraction, all of which change what a number means. If a result and your experience disagree, that is a conversation to have, not a settled verdict. And none of this is a reason to change anything on your own: dose and monitoring decisions belong with your clinician, and laboratory ranges are specific to the testing lab.
This is the short version. The full evidence — every target range graded, with the SHBG and free-fraction problem set out in detail — is in the companion Evidence Review →
Key sources. The evidence points here rest on a 2025 systematic review of oestradiol concentrations for feminising therapy (Winston-McPherson et al., LGBT Health); laboratory-monitoring and narrative reviews by Nolan and Cheung (Clinical Chemistry, 2025; Transgender Health, 2021); the Endocrine Society (2017) and WPATH Standards of Care, Version 8 (2022) guidelines; Vermeulen’s validation of calculated free testosterone (1999); and the ESTHER route-of-oestrogen thrombosis data (Canonico et al., 2007). Full references for every claim are in the companion Evidence Review.