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Estradiol

Principle

Estradiol is produced by the adrenals, placenta, and testes, and is the principal estrogen secreted by the ovaries. Over 98% of circulating estradiol is bound to serum proteins, mainly sex hormone-binding globulin (SHBG). Metabolic clearance of estradiol is influenced by conversion to estrone, hydroxylation, and conjugation with sulfate or glucuronide.

Estradiol normally exerts negative feedback on gonadotropin release. However, as estradiol production accelerates with the rapid growth of the dominant follicle, this feedback becomes positive, triggering a surge in LH secretion and ovulation. Measurement of estradiol is useful in evaluating menstrual dysfunctions, including delayed puberty, amenorrhea, and menopause.

Specimen Requirements

Specimen

Serum (serum separator tube, SST)

Collection

Allow clotting for 30 minutes; centrifuge 10 minutes at ~1000 g; transfer serum to a separate plastic vial. Ensure no red blood cells are present.

Processing

Allow clotting for 30 minutes; centrifuge 10 minutes at ~1000 g; transfer serum to a separate plastic vial. Ensure no red blood cells are present.

Storage and Transport

≤ –20 °C; avoid repeated freeze–thaw cycles. For short-term storage (≤8 hours), samples may be kept at room temperature (15–30 °C); for up to 48 hours, refrigerate at 2–8 °C.

Unacceptable Specimens

Hemolyzed or unspun specimens (may yield inaccurate results)

Method

Enhanced chemiluminescence.

Normal Range

Category	Estradiol (pg/mL)
Female, mid-follicular	27–122
Female, peri-ovulatory peak	95–433
Female, mid-luteal	49–291
Postmenopausal female	<20–40

Turnaround Time

3 days

References

Yen SSC, Lein A. The Apparent Paradox of the Negative and Postitive Feedback Control System on Gonadotropin Secretion. Am J Obstet Gynecol. 126:942-954.

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