Estradiol

Estradiol is the main estrogen the body makes, and the one used in feminizing hormone therapy. It is chemically identical to the hormone produced by ovaries, which is why it is sometimes described as "bioidentical". Spelled oestradiol in the UK.

Where you'll meet it

On every feminizing prescription, and on blood results, where the estradiol level is one of the two numbers (with testosterone) that prescribers watch most. It also turns up on masculinizing blood results, because the body turns some testosterone into estradiol; that is normal, and a moderate level is part of what protects bone.

What it does

Estradiol drives the changes of an estrogen-led puberty: breast growth, softer skin, fat moving towards hips and thighs, and slower, finer body hair. It also protects bone, which is why nobody should be left for long without either estrogen or testosterone. It does not do everything on its own: it lowers testosterone, but not always far enough, which is where an anti-androgen comes in. Changes timeline covers what changes and when.

The forms

• Tablets: swallowed, or held under the tongue (sublingual), which some prescribers suggest and others do not. The cheapest form.
• Patches, gel and spray: through the skin (transdermal), often preferred for people over 40 or with clot risk factors, because they skip the liver.
• Injections: estradiol valerate or cypionate, into muscle or under the skin, every few days to every couple of weeks depending on the type. Common in parts of the US, less often prescribed on public systems elsewhere.
• Implants: small pellets under the skin, offered by a few UK clinics and uncommon now.

The words "valerate", "cypionate" and "hemihydrate" name an attached chemical that changes how the estradiol is absorbed or released. Once in the body, it is the same hormone. In the US, tablets typically cost somewhere around $10 to $40 a month self-pay and patches a good deal more; cost and insurance has the ranges.

Not the same as the pill

Contraceptive pills contain ethinylestradiol, a synthetic estrogen with a higher clot risk, and it does not even show up on a standard estradiol blood test. It is not recommended for feminizing HRT. If you are offered it, ask why. Estrogen explains why guidelines moved away from it and from conjugated equine estrogens (Premarin).

Reading the level

Estradiol is reported in pmol/L in the UK, Europe and Australia and in pg/mL in the US; divide pmol/L by about 3.67 to get pg/mL. Guidelines such as the Endocrine Society's commonly cite a target of roughly 100 to 200 pg/mL (about 370 to 730 pmol/L) on feminizing hormones, alongside testosterone under about 50 ng/dL. Your prescriber sets your own target.

What the level means depends on when the sample was taken relative to your last dose, the peak and trough. With injections and sublingual tablets especially, the same person can look high one day and low a week later. How to read your hormone blood results walks through it.

Common questions

Higher is faster. Past the target range, more estradiol adds clot risk without adding feminization in any reliable way.

Bioidentical means risk-free. It means identical to the body's own hormone. It still raises DVT risk, especially by mouth.

The lab flag means something is wrong. The reference range is usually for the sex on your record, not for someone on HRT.

What to ask

Which form suits my age and clot risk? When in my dosing cycle should my blood be taken? What estradiol and testosterone figures are you aiming for, in which units? If supply of my usual form runs short, what is the backup?

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