Free Estradiol (Sensitive)
This test measures the free (unbound to SHBG or albumin) estradiol and total sensitive estradiol in blood. The test is performed using liquid chromatography/mass spectrometry (LC/MS). NOTE: This test is a send out test to Quest's Nichols Institute San Juan Capistrano. Testing schedule is Mon and Wed. Reports are available within 4-14 days from the time the specimen is received at the send out testing lab. Test results may take up to 16 business days.
This test uses liquid chromatography/mass spectrometry to accurately measure free estradiol, the portion of estradiol that is not bound by SHBG. NOTE: This test is a send out test to Quest's Nichols Institute San Juan Capistrano. Testing schedule is Mon and Wed. Reports are available within 5-14 business days from the time the specimen is received at the send out testing lab.
The free estradiol test, also sometimes referred to as "bioavailable" estradiol, measures the portion of estradiol that is not bound to proteins in the bloodstream and is thus free to exert its effects on the body.
In the bloodstream, most estradiol is bound to a protein called sex hormone-binding globulin (SHBG), and a smaller amount is bound to albumin. Only a tiny fraction (about 1-3%) is unbound, or "free." This free fraction, along with the portion loosely bound to albumin, is often considered the "bioavailable" estradiol, as it can readily diffuse into tissues and bind to estrogen receptors to exert its physiological effects.
The measurement of free or bioavailable estradiol can sometimes provide more useful information about hormone status than total estradiol. For example, conditions that alter SHBG levels, such as hyperthyroidism, liver disease, or obesity, can affect the total amount of estradiol in the bloodstream without necessarily affecting the amount of bioavailable estradiol.
Therefore, in some cases, it might be more informative to measure free or bioavailable estradiol. It can provide a better indication of the amount of active estradiol in the body, which can be important in assessing various conditions related to fertility, menstrual irregularities, symptoms of menopause, and in the management of hormone replacement therapy or transgender hormone therapy. However, whether to measure total, free, or bioavailable estradiol would be determined by a healthcare provider based on individual circumstances.
Note: Studies on the effect of free estradiol blood levels in men are lacking. Only one reference concludes that free estradiol, not total, maybe a better predictor of bone density in older men (J Bone Miner Res 2005;20:1334–1341.)
Some physicians are starting to use this test in men with low Sex Hormone Binding Globulin with symptoms of high estradiol.
For more information about estradiol, read our blog posts
Free Estradiol, Percent
Reference Ranges (%)
Age Range
Adult Males 1.7 - 5.4
Adult Females 1.6 - 3.6
Free Estradiol, Serum
Reference Ranges (pg/mL)
Age Range
Adult Males 0.2 - 1.5
Adult Females 0.6 - 7.1
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