What Monitoring Is For: The Safety System That Makes Continuous Care Possible — Anatomy of Good Care (3/7)

What monitoring is actually for

There is a way of thinking about monitoring that treats it as a checkpoint — a periodic permission slip the patient has to earn to keep their treatment. That framing gets it backwards. The reason a clinic monitors is not to decide whether to allow care to continue; it is to make continuous care safe enough that it never has to stop unnecessarily. Good monitoring is the infrastructure of continuity, not an obstacle to it.

Once you see it that way, the difference between cheap monitoring and good monitoring comes into focus. The cheap version does the legal minimum, on the longest interval it can defend, and reads each result as a pass/fail against a target. The version built around the patient asks a harder question at every visit: what could actually harm this person, is it happening, and does this number mean what it appears to mean? Those are not the same activity, and they do not cost the same — but the difference is mostly time and attention, not money.

Estradiol-based care: the safety lives partly in the route

The familiar targets are real. The Endocrine Society and WPATH advise titrating feminizing therapy to suppress testosterone to roughly the cisgender female range (below about 50 ng/dL) while keeping estradiol broadly within the physiological premenopausal range (around 100–200 pg/mL) [1][2]. Worth holding lightly, though: UCSF’s guidance notes that the estradiol target rests largely on expert opinion, may be overly conservative, and that there is no good evidence that pushing estradiol higher produces more feminization once androgens are adequately suppressed [3]. So the goal is adequate estrogen and genuine androgen suppression — not the largest estradiol number obtainable.

The deeper safety decision in estrogen care is one a numbers-only approach misses entirely: the route. Oral estrogen passes first through the liver, where it shifts the clotting balance — raising procoagulant factors and lowering natural anticoagulants — while transdermal estradiol has minimal effect on those pathways [7]. The clinical consequence is consistent: transdermal 17β-estradiol has the most favourable thrombotic safety profile among the commonly used formulations and is preferred, particularly for anyone with venous-thromboembolism risk factors [2][6]. Two formulations are specifically to be avoided — ethinyl estradiol, associated in one cohort with a roughly 45-fold increase in VTE at high dose alongside cyproterone, and no longer recommended in contemporary gender-affirming care for that reason; and high-risk progestin combinations [6][7]. (The oral-versus-transdermal contrast is quantified most precisely in cisgender menopausal cohorts — oral estrogen carrying an elevated VTE odds ratio while transdermal sits at roughly no excess — but the hepatic mechanism is the same one operating in trans patients.) The reassuring counterweight, which the patient deserves to hear in the same breath: on modern estradiol regimens the absolute risk remains low [6].

This is also where the honesty about over-testing belongs. Routine thrombophilia screening before starting estrogen is not recommended — clinical risk factors predict better than the panel does, and a reflexive screen mostly generates anxiety and cost [8]. Choosing the safer route and asking the right history is worth more than a battery of pre-emptive labs. Best care is not the longest test list.

Two more belong on the estrogen panel for the right reasons. Prolactin earns periodic attention because estrogen stimulates the pituitary cells that produce it and rare prolactinomas have been reported; guidelines vary, but several recommend periodic monitoring, with particular relevance for anyone using cyproterone [9]. And bone: because, as covered elsewhere in this series, a patient who has had a gonadectomy depends entirely on their hormone supply for skeletal protection, which makes adherence and appropriately targeted bone surveillance a genuine safety issue rather than an afterthought [3].

A word on the number itself

Here is where a maximalist instinct and a thoughtful one part ways. It is true — and important — that a total estradiol level can mislead. Sex-hormone-binding globulin binds estradiol, and when SHBG is high (which oral estrogen itself raises, more than transdermal does), the total can read on-target while the biologically available fraction does not [4]. That is a real phenomenon and a real reason a single number should never be read in isolation.

But the conclusion that follows is not “measure free estradiol at every visit.” Free-estradiol assays are not well standardised, direct measurement requires specialised methods reserved for protein-binding problems, and no guideline treats routine free-E2 as standard [4]. If anything, the current direction of travel questions our over-reliance on the estradiol number at all — recent work suggests testosterone tracks clinical variables more reliably than estradiol in feminizing care, with LH a reasonable surrogate after orchiectomy [5]. The sophisticated move is therefore not to add a reflex test to every draw, but to read the estradiol in context — against testosterone, against SHBG when the picture and the number disagree, and above all against how the patient actually presents. The number serves the patient. It is not the patient.

Testosterone-based care: the value that’s easy to forget

For masculinizing therapy the headline target is straightforward — testosterone titrated into the mid-normal male range — but arguably the most important routinely monitored safety value is the one a rushed review skips: the haematocrit. Testosterone raises haemoglobin and haematocrit in a dose- and level-dependent way, and the resulting erythrocytosis is the best-documented serious risk of the treatment, because marked erythrocytosis increases blood viscosity and is associated with increased thrombotic risk [6]. It is monitored from baseline, rechecked in the early months and then at least annually, and it is acted on as it climbs into the mid-50s percent — usually by adjusting dose, spacing or formulation rather than stopping outright [6]. Injectable testosterone tends to push it higher than transdermal, which is itself a monitoring-informed reason a formulation might be changed [6].

The timing of the draw matters as much as the test, and what counts as the right time depends on the formulation. For injected esters, a level taken at the wrong point in the cycle is not a clean read; sampling at the appropriate interval is part of what makes the number mean anything. Alongside this sit lipids and blood pressure, both of which testosterone can move, and — again — bone, which carries particular weight for anyone who has had an oophorectomy and therefore depends on continued testosterone for skeletal protection [3].

The shared floor, and the part that costs time

Underneath both pathways is a common-sense safety layer that has nothing to do with gender: blood pressure, weight, a metabolic and lipid picture, renal and liver function where the regimen warrants it, and — crucially — the continuation of ordinary age-appropriate screening that a person remains eligible for. None of this is exotic. It is simply done, on a sensible rhythm: the Endocrine Society’s suggested cadence — typically around every three months through the first year, then once or twice a year — exists because the early period is when doses settle and problems surface [1]. Laboratory results are only one part of the picture in any case — they are read alongside symptoms, examination where indicated, adherence, side effects and the person’s own goals for treatment, none of which a number can replace.

And then there is the part that separates good monitoring from cheap monitoring, and it is not a test at all. It is what happens to the results. The cheap version files them — a letter in three weeks, a number out of context, a normal range the patient never sees. The version built around the patient does the expensive thing: it puts the results in front of the person the same day, in plain language, as their information rather than a lab report; it reads the number against how they actually feel, not instead of it; and it makes any adjustment with them. That costs time and attention. It costs almost nothing else. And it is the first thing to be cut when a service is organised around its own convenience rather than the person in the chair.

The point

Monitoring done well is not surveillance of the patient. It is the clinic demonstrating, visit after visit, that continuity is safe — that care can run without interruption precisely because someone is watching the things that would justify a change before they become a crisis.

The cheapest thing to skip is always the conversation: the explaining, the contextualising, the deciding-together. It is also the thing that mattered most. A number measured and never understood has monitored nothing. The measure of good monitoring is not how many boxes were ticked or how little it cost — it is whether the person walked out knowing what their own body is doing, and why the plan is what it is.

Sources

1. Hembree WC et al. Endocrine Treatment of Gender-Dysphoric/Gender-Incongruent Persons: An Endocrine Society Clinical Practice Guideline. Journal of Clinical Endocrinology & Metabolism, 2017; 102(11):3869. — Feminizing targets (estradiol ~100–200 pg/mL premenopausal range; testosterone suppression <50 ng/dL); monitoring cadence of roughly every 3 months in the first year then 1–2×/year; route options. (Adults.)
2. World Professional Association for Transgender Health, Standards of Care version 8 (2022). — Same sex-steroid targets; transdermal 17β-estradiol or estradiol valerate preferred for those with VTE risk factors; ethinyl estradiol not recommended. (Adults.)
3. UCSF Gender Affirming Health Program, Guidelines for the Primary and Gender-Affirming Care of Transgender and Gender Nonbinary People (feminizing therapy overview; bone health and osteoporosis). — Estradiol target is expert-opinion-based and possibly overly conservative; no evidence that higher estradiol adds feminization once androgens are suppressed; hormone underutilisation after gonadectomy as an osteoporosis risk. (Trans-specific; adults.)
4. ARUP Consult, Endocrine Testing in Transgender Adults; Stangl TA et al., The influence of gender-affirming hormone therapy on serum concentrations of hormone-binding proteins, European Journal of Endocrinology, 2025; 192(5):614–620; and the case analysis Approach to Nonsuppressed Testosterone in Transgender Women Receiving Gender-Affirming Feminizing Hormonal Therapy, Journal of the Endocrine Society, 2021; 5(9):bvab068. — SHBG affects estradiol measurement (a high SHBG can leave total estradiol on-target while the available fraction is not); free-estradiol/SHBG testing is a targeted second-line tool for discordant cases, not a routine measure; oral estradiol raises SHBG more than transdermal. (Trans-specific; adults.)
5. Choice of Hormone Assay to Monitor Feminizing Gender-Affirming Hormone Therapy. Endocrine Practice, 2025; PMID 40945660 (Mount Sinai; cross-sectional analysis of 9,916 transfeminine individuals). — Suggests possible over-reliance on the estradiol assay; testosterone more consistently associated with clinical variables (age, orchiectomy, spironolactone use), and LH a reasonable surrogate after orchiectomy; estradiol most useful for identifying overtreatment. (Trans-specific; emerging evidence, not yet consensus.)
6. Testosterone safety and VTE/route: Bhasin S et al, Testosterone Therapy in Men With Hypogonadism: An Endocrine Society Clinical Practice Guideline, JCEM 2018; 103(5):1715 (testosterone raises haematocrit dose-dependently; erythrocytosis monitoring, intervention as haematocrit exceeds ~54%); plus trans-specific erythrocytosis management data (testosterone formulation, dose-spacing); and Gender-affirming hormone therapy in the transgender patient: influence on thrombotic risk, ASH Education Program, 2024 (ethinyl estradiol ~45-fold VTE increase at high dose with cyproterone; transdermal estradiol least thrombogenic; absolute risk on modern regimens low). (Mix of adults / trans-specific; testosterone target range from the male-hypogonadism guideline.)
7. Mechanism of route-related VTE risk: Managing the risk of venous thromboembolism in transgender adults undergoing hormone therapy (PMC6628137); and Risk of venous thrombosis with oral versus transdermal estrogen therapy among postmenopausal women (PubMed 20601871). — Oral estrogen undergoes first-pass hepatic metabolism, raising procoagulant factors and lowering anticoagulants; transdermal has minimal haemostatic effect; in cisgender cohorts oral estrogen carries an elevated VTE odds ratio while transdermal sits at roughly no excess. (Mechanism trans-relevant; the quantified odds ratios are from cisgender menopausal women — flagged.)
8. VTE risk in transgender women on estrogen therapy (ASH/Blood, 2025). — Transdermal preferred; routine thrombophilia screening before initiation not recommended (clinical risk factors more predictive); primary anticoagulant prophylaxis not indicated. (Trans-specific; adults.)
9. Nolan BJ, Accatino MI, Angus LM, Cheung AS. Approach to prolactin monitoring and hyperprolactinaemia in transgender and gender-diverse individuals undergoing gender-affirming hormone therapy. Frontiers in Endocrinology, 2025; 16:1608108; doi:10.3389/fendo.2025.1608108. — Estrogen stimulates pituitary lactotrophs; some guidelines recommend periodic prolactin monitoring, with particular relevance for cyproterone users. (Trans-specific; adults.)