Estradiol, Bioavailable, Mass Fraction, Serum or Plasma
This test measures the portion of estradiol in the blood that is not tightly bound to carrier proteins and is therefore free to enter tissues and exert hormone effects.
["Bioavailable estradiol estimates how much of this estrogen is readily available to act on the body's tissues."]
Key facts at a glance
- LOINC
- 13883-4
- Short code
- Estradiol Bioavail MFr SerPl
- Synonyms
- Estradiol Bioavail MFr SerPl
- Category
- chemistry
- Sample
- serum
- Container
- Red-top tube (SST)
- Units
- N/A
- Ref low
- 20
- Ref high
- 400
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- 18–65 years
- CPT
- 82670
- SNOMED
- 300919004
- Specimen volume
- 5 mL
- Stability
- Room temperature: 4h, Refrigerated: 24h, Frozen: 7d
- Hemolysis max
- 500
- Lipemia max
- 1000
- Icterus max
- 500
- TAT
- 4–24 hours
- Order
- routine
What Is Being Measured
Estradiol is the main form of estrogen. In the bloodstream, most estradiol is attached to proteins such as sex hormone-binding globulin (SHBG) and albumin. Only the unbound and loosely bound portion, called bioavailable estradiol, can readily leave the blood and act on tissues. This test estimates that bioavailable fraction rather than total estradiol.
Why the Test Is Ordered
Clinicians may order bioavailable estradiol when total estradiol results do not fully explain symptoms or when protein binding is expected to be abnormal. Because SHBG levels can shift with age, weight, liver conditions, thyroid disease, and some medications, the bioavailable fraction can differ from what total estradiol alone would suggest.
How the Test Is Done
A blood sample is collected from a vein, usually in your arm. The laboratory measures estradiol and related binding proteins, then calculates the bioavailable portion. Your provider will tell you whether any preparation, such as timing relative to your menstrual cycle, is needed.
What Results Mean
Results are interpreted alongside your symptoms, age, sex, menstrual status, and other hormone tests. A higher or lower bioavailable estradiol does not by itself diagnose a condition. Your care team will consider the whole picture, and reference ranges vary by laboratory and population.
Reference range
Premenopausal: 20-400 pg/mL; Postmenopausal: <30 pg/mLN/A
For females: inform if menstrual cycle status. For certain tests, timing within menstrual cycle may matter.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
Bioavailable estradiol can be useful in evaluating estrogen-related concerns such as menstrual irregularities, fertility, signs of hormone excess or deficiency, and conditions where SHBG is altered. It is a calculated estimate rather than a direct measurement, so it complements rather than replaces total estradiol and clinical judgment. Interpretation should always be individualized.
Short name
Bioavailable Estradiol
Frequently asked questions
Does this test require fasting or special timing?
Is bioavailable estradiol the same as free estradiol?
Can I interpret the result on my own?
Sources
- 1
- 2Lab Tests OnlineSource
- 3
Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.
This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.
This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.
If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.
Medically reviewed by WellAlly Editorial Team Last reviewed August 16, 2026. · Read our editorial policy