Estradiol

What it is

Estradiol (E2) is the principal estrogen during reproductive life, produced primarily by ovarian granulosa cells, with smaller contributions from adrenal precursors and aromatisation of testosterone in adipose tissue.

Reference ranges

• Follicular phase: 30–120 pg/mL.
• Mid-cycle ovulatory peak: 130–370.
• Luteal phase: 70–250.
• Post-menopause (untreated): typically <20.
• HRT (oral or transdermal): maintain in a range that controls symptoms; many practitioners target 40–100 in established post-menopausal HRT.

Why it matters

• Cycle monitoring, infertility evaluation.
• Diagnosis of premature ovarian insufficiency.
• Guidance for menopausal HRT dosing.
• Surveillance for hormone-sensitive cancers (e.g. aromatase-inhibitor monitoring).

In men

Excess aromatisation in obesity can produce inappropriately high estradiol with downstream effects (gynecomastia, low libido). Very low estradiol in men is also associated with reduced bone mineral density.

Caveats

• Salivary and capillary tests are poorly standardised.
• Single-time-point readings in menstruating women are uninterpretable without cycle context.
• Mass-spec assays are most reliable; immunoassays are widely used but noisier at low concentrations.

Related entries

HRT, Osteoporosis, Cardiovascular disease.