This assay measures both total estradiol and the biologically active free fraction of estradiol using equilibrium dialysis—the gold-standard method for separating protein-bound from unbound hormone—followed by quantification via high-performance liquid chromatography tandem mass spectrometry (HPLC/MS-MS). Free estradiol represents the small percentage (~1–3%) of circulating estradiol not bound to sex hormone-binding globulin (SHBG) or albumin, and is considered the hormonally active moiety available to target tissues. This combined panel provides a comprehensive assessment of estrogen status, particularly valuable when SHBG levels are abnormal. Estradiol (E2) is the predominant and most potent endogenous estrogen, synthesized primarily in the ovarian granulosa cells in premenopausal women and via peripheral aromatization of androgens in postmenopausal women and men. The majority of circulating estradiol is bound to SHBG (~38%) and albumin (~60%), with only ~2% circulating as free, bioavailable hormone capable of binding estrogen receptors (ERα and ERβ) to exert genomic and non-genomic effects on reproductive, skeletal, cardiovascular, and central nervous system tissues. Conditions that alter SHBG concentrations—such as obesity, thyroid dysfunction, liver disease, or exogenous hormone use—can significantly dissociate total from free estradiol levels, making free estradiol measurement clinically informative.
This test measures both the total amount of estradiol (a key estrogen hormone) in your blood and the small 'free' portion that is not attached to proteins and is therefore active in your body. Most estradiol is carried by proteins in the blood and cannot act on your cells; only the free portion can. Measuring the free fraction gives a more accurate picture of how much estrogen is actually available to your tissues, especially if your protein levels are unusual. This information helps your doctor evaluate hormonal balance, bone health, reproductive function, and symptoms related to too much or too little estrogen.
When elevated: Elevated free estradiol may indicate estrogen excess states, which can be associated with gynecomastia in males, menstrual irregularities or endometrial hyperplasia in females, suppression of the hypothalamic-pituitary-gonadal axis, and increased risk of estrogen-sensitive malignancies with chronic exposure. When low: Low free estradiol may be associated with symptoms of estrogen deficiency including vasomotor symptoms, urogenital atrophy, decreased bone mineral density, mood disturbances, and impaired cardiovascular protection, particularly in postmenopausal women and hypogonadal individuals.
Free estradiol is relevant to athletes because training, energy availability, and body composition all influence SHBG levels and thus the ratio of free to total estradiol. Low energy availability or very low body fat can suppress estradiol and increase injury risk and menstrual dysfunction in female athletes; conversely, obesity can lower SHBG and raise free estradiol. This test is more informative than total estradiol alone when interpreting hormonal status in athletes with atypical SHBG due to training intensity, diet, or body composition extremes.
Fasting Required
No
Method
Liquid chromatography tandem mass spectrometry (LC/MS/MS); equilibrium dialysis
verifiedGold StandardMass spectrometry — higher accuracy, especially at low concentrations
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$75.00$135
1.8× less than retail
Versus the typical direct-to-consumer retail price for this test (illustrative — consumer prices vary by provider and region).
$75.00
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