Estradiol (E2)

What it measures, and what changes the number.

Estradiol is the main and most potent estrogen. It is produced mainly by the ovaries, and in smaller amounts by the testes, adrenal glands and fat tissue through conversion of testosterone. The test measures estradiol in serum and is reported in pmol/L or pg/mL.

It is commonly ordered with FSH, LH and progesterone to look at the reproductive axis, and with total testosterone and SHBG, since much estradiol travels bound to SHBG.

In people who menstruate, estradiol changes markedly across the cycle, so the cycle day of collection matters. Method also matters: standard immunoassays can be less accurate at low concentrations and are subject to some interferences, which is why labs offer ultrasensitive tests by LC/MS (mass spectrometry). Results from different methods may not be directly comparable. Labs may print it as 17 beta Estradiol or ESTRADIOL,ULTRASENSITIVE, LC/MS.

Reference ranges labs publish

Each lab states an interval for its own method and the population it measured. They differ, they are not interchangeable, and none of them is a verdict on a single result.

Usually reported in pmol/L or pg/mL.

Often read alongside: FSH, LH, Progesterone, Total testosterone, SHBG

Calculators that use it: Testosterone to estradiol ratio, DHT to estradiol ratio

Blood test glossary