TL;DR
- The 100–200 pg/mL oestradiol target was derived from physiologic concentrations in premenopausal women and expert consensus — not from outcome trials in trans women
- A 2025 systematic review found no studies demonstrating this range optimises feminisation or reduces adverse events
- Being within range does not mean your HRT is optimised; being above range does not automatically mean something is wrong
- Critically: the absence of evidence supporting 100–200 pg/mL does not mean higher concentrations improve outcomes or carry equivalent long-term safety
- The range is best understood as a pragmatic consensus target, not a rigid boundary — but clinical context cuts both ways
Many trans women are told to keep oestradiol between 100 and 200 pg/mL. This number appears in Endocrine Society recommendations, in WPATH SOC-8, and in most clinical protocols. In some clinical settings, values above this range are treated as inherently excessive rather than interpreted in context. The question worth asking is: how strong is the evidence behind it?
Where the range came from
The 100–200 pg/mL target was largely extrapolated from physiologic oestradiol concentrations observed in premenopausal cisgender women, combined with expert consensus aimed at avoiding supraphysiologic exposure. It was not derived from controlled trials in trans women evaluating feminisation outcomes, testosterone suppression, safety, or wellbeing. The range reflects an attempt to approximate normal female physiology rather than a target established through direct outcome evidence.
What the evidence actually shows
A 2025 systematic review (Winston-McPherson et al.) evaluated 49 studies over a 24-year period specifically to assess whether the 100–200 pg/mL range was associated with optimal feminising outcomes or reduced adverse events in trans women. It found no studies demonstrating that this range provides optimal feminisation or reduces adverse events, and concluded that evidence does not support using this guideline range as an indicator of sufficient feminisation.
Separately, research has shown that guideline-concordant prescribing — doses written exactly as guidelines recommend — frequently produces oestradiol levels outside the target range in practice. In Carlson et al., below-range oestradiol levels were frequently observed with standard transdermal doses, while above-range levels were frequently observed with standard parenteral doses.
What this means — and what it does not
Being within range does not mean your HRT is optimised. Being above range does not automatically mean something is wrong. The full clinical picture — oestradiol level, testosterone level, route of administration, symptoms, and individual response — matters more than whether a single number falls within a population-derived bracket.
A person on injectable oestradiol with a measured level of 250 pg/mL — appropriately interpreted in relation to injection timing — and testosterone suppressed to target may have achieved satisfactory clinical results. A person on oral oestradiol with oestradiol at 150 pg/mL and testosterone persistently above target has not — regardless of being within range. Interpretation is also affected by route, assay method, and timing of blood draw, particularly for injectable oestradiol, where peak and trough concentrations can differ substantially.
However, the symmetry here is critical: the absence of evidence supporting 100–200 pg/mL as an optimal target does not constitute evidence that higher concentrations improve outcomes or carry equivalent long-term safety. The same evidentiary gap that weakens the case for the guideline range also means we cannot confidently say that 250 pg/mL produces better feminisation than 150 pg/mL, that higher levels improve wellbeing, or that sustained concentrations well above commonly accepted physiologic targets are equally safe over the long term. Safety data above physiologic levels remain sparse, and avoiding supraphysiologic concentrations is considered prudent on precautionary grounds even in the absence of a proven danger threshold.
How to think about the range
The 100–200 pg/mL target is best understood as a pragmatic consensus target rather than a rigid boundary — but clinical context applies in both directions. It is neither a guarantee of adequate therapy when achieved, nor an evidence-based ceiling beyond which outcomes are established to be worse. What it represents is a reasonable approximation of normal female physiology, used as a starting point for clinical judgment in the absence of better trial data.
The appropriate response to weak guideline evidence is not to dismiss the guideline, but to apply it with the nuance it deserves: monitoring the full hormone panel, assessing clinical response, and adjusting based on the individual — rather than treating a population-derived number as either a guaranteed target or an absolute limit.
⚠️ Clinical note: The evidentiary critique of the 100–200 pg/mL range is legitimate and increasingly discussed in the literature. It does not support routinely exceeding the range. It supports applying it as a pragmatic guide rather than a rigid rule, with clinical judgment and full panel assessment driving decisions.
Sources
- Winston-McPherson GN, Thomas TA, Krasowski MD, et al. Estradiol Concentrations for Adequate Gender-Affirming Feminizing Therapy: A Systematic Review. LGBT Health. 2025;12(7):477–489.
- Hembree WC, Cohen-Kettenis PT, Gooren L, et al. Endocrine Treatment of Gender-Dysphoric/Gender-Incongruent Persons: An Endocrine Society Clinical Practice Guideline. J Clin Endocrinol Metab. 2017;102(11):3869–3903.
- Coleman E, Radix AE, Bouman WP, et al. Standards of Care for the Health of Transgender and Gender Diverse People, Version 8. Int J Transgend Health. 2022;23(Suppl 1):S1–S259.
- Carlson SM, Dominguez C, Jeevananthan A, Crowley MJ. Follow-Up Estradiol Levels Based on Regimen Formulation With Guideline-Concordant Gender-Affirming Hormone Therapy. J Endocr Soc. 2025;9(3):bvae205.
