Estradiol (E2), Serum
The Estradiol (E2) Serum test measures 17β-estradiol — the most potent endogenous oestrogen — in serum, providing the primary quantitative marker of ovarian follicular function, oestrogenic status, and exogenous oestrogen pharmacokinetics. Interpretation is cycle-phase-dependent and requires concurrent documentation of menstrual cycle day, menopausal status, and current oestrogen therapy.
1
Biomarkers
Blood (serum)
Sample
1–3 business days
Turnaround
No — fasting is not required for serum estradiol. However, collection timing relative to the menstrual cycle phase is the critical variable: for ovarian reserve assessment, collect on cycle day 2–3 (day 1 = first day of full flow); for ovulatory confirmation, collect at the expected mid-cycle peak; for corpus luteum and luteal phase adequacy, collect 7 days before the anticipated next menstruation (approximately day 21 of a 28-day cycle). For HRT monitoring, collect at a standard timing relative to dose — typically 24 hours after transdermal patch application or application of gel/spray for trough level; practitioners managing HRT should specify desired collection timing.
Fasting
What is the Estradiol (E2) test?
The Estradiol (E2) Serum test quantifies 17β-estradiol — the primary and most biologically active endogenous oestrogen — in serum, providing a direct measurement of oestrogenic status from ovarian, peripheral, or exogenous sources that is the cornerstone of female reproductive endocrinology and hormone replacement therapy management. Estradiol measurement is clinically informative only when interpreted in the context of the menstrual cycle phase (for premenopausal women), menopausal status, and the clinical question being asked — the same numerical estradiol value carries profoundly different clinical implications at day 3 of the cycle, at the mid-cycle LH surge, in the luteal phase, and in a postmenopausal woman on HRT. Estradiol serves as the primary quantitative oestrogen marker across several distinct clinical domains simultaneously. In reproductive medicine and fertility assessment, estradiol characterises ovarian follicular development and is an essential component of the cycle day 2–3 ovarian reserve panel alongside FSH and AMH; abnormally elevated day-3 estradiol (above 60–80 pg/mL) suppresses FSH through negative feedback and can mask an elevated FSH that would otherwise reveal diminished ovarian reserve. During ART and ovulation induction, serial estradiol provides real-time folliculogenesis monitoring, with each dominant follicle contributing approximately 200–300 pg/mL to peak estradiol concentration — predicting the number of mature follicles and guiding trigger timing. In the perimenopausal transition, erratic and declining estradiol — oscillating above and below reproductive-age reference ranges — alongside rising FSH maps the hormonal trajectory from perimenopause to menopause. In HRT management, estradiol provides the therapeutic drug monitoring endpoint for transdermal, oral, vaginal, and implant oestrogen delivery, with target levels titrated to symptom relief, bone density protection, and cardiovascular risk minimisation.
What does the Estradiol (E2) test measure?
17β-Estradiol is the most potent endogenous oestrogen and the primary oestrogenic steroid in premenopausal women. It is synthesised predominantly by granulosa cells of developing ovarian follicles through aromatisation of testosterone under FSH stimulation via the enzyme aromatase (CYP19A1) — a reaction requiring androstenedione or testosterone as substrate. During the menstrual cycle, estradiol rises progressively through the follicular phase as the dominant follicle develops, peaks sharply at the mid-cycle LH surge (the ovulatory peak) reaching 200–400 pg/mL or higher in stimulated cycles, falls briefly at ovulation, rises again during the luteal phase under corpus luteum support, then falls precipitously before menstruation. In postmenopausal women, ovarian follicular oestrogen production ceases, with residual circulating estradiol derived from peripheral aromatisation of adrenal androgens — predominantly androstenedione — in adipose tissue, liver, muscle, and skin. Estradiol exerts its biological effects through nuclear oestrogen receptors ERα and ERβ, and membrane-associated receptors including GPER1, regulating hundreds of gene targets across reproductive, skeletal, cardiovascular, neurological, and metabolic tissues. Its plasma half-life is approximately 1–2 hours.
Serum estradiol is the primary quantitative marker of ovarian follicular function, oestrogenic status, and exogenous oestrogen exposure across all stages of female reproductive life. Its clinical applications span a broad range: in fertility assessment and ART, estradiol on cycle day 2–3 characterises ovarian reserve alongside FSH and AMH — values above 80 pg/mL on early follicular day suggest advanced follicular recruitment and may indicate poor ovarian reserve despite normal or low FSH; during controlled ovarian stimulation, serial estradiol monitoring guides gonadotropin dose adjustment and timing of trigger injection; in cycle evaluation, cycle-phase-specific estradiol confirms follicular development, ovulation, and corpus luteum adequacy; in perimenopause transition, declining and erratic estradiol alongside rising FSH characterises the hormonal landscape of menopause approach; in hormone replacement therapy management, estradiol guides initial dosing and serial dose titration to symptom relief and bone protection targets; and in male assessment, estradiol screens for peripheral aromatisation excess in obesity, liver disease, and hypogonadism management.
Why is the Estradiol (E2) test ordered?
- Ovarian reserve assessment — early follicular phase (day 2–3) estradiol alongside FSH and AMH to characterise ovarian reserve in patients planning fertility treatment, with elevated day-3 estradiol (>60–80 pg/mL) masking FSH elevation and indicating advanced follicular recruitment despite apparently normal FSH
- Controlled ovarian stimulation monitoring — serial estradiol during gonadotropin stimulation for IVF or IUI to guide dose adjustment, predict multifollicular response, assess OHSS risk, and determine timing of hCG or GnRH agonist trigger
- Menstrual cycle characterisation — cycle-phase-specific estradiol to confirm follicular development, identify anovulatory cycles with persistently low estradiol, assess corpus luteum function in the luteal phase, and evaluate oestrogen-deficient states in hypothalamic amenorrhoea and premature ovarian insufficiency
- Perimenopause and menopause transition assessment — erratic estradiol alongside rising FSH to characterise the hormonal landscape of the perimenopausal transition and confirm the hormonal definition of menopause (FSH >25–30 IU/L with oestrogen withdrawal) in patients with amenorrhoea of uncertain duration
- Hormone replacement therapy initiation and monitoring — baseline estradiol before HRT commencement, with serial monitoring 6–12 weeks after initiation and after dose changes to confirm therapeutic range achievement on transdermal, oral, subcutaneous, or vaginal delivery
- Premature ovarian insufficiency (POI) and primary ovarian insufficiency evaluation — low estradiol with markedly elevated FSH (>25 IU/L) in women under 40 with oligo-amenorrhoea confirms the biochemical pattern of POI, requiring bone health assessment and urgent HRT discussion
- Male hypogonadism and gynaecomastia workup — estradiol in males to assess peripheral aromatisation excess contributing to gynaecomastia, adiposity-related oestrogen excess suppressing endogenous testosterone, and to guide aromatase inhibitor use in testosterone replacement monitoring
- Integrative and functional medicine female hormone optimisation — estradiol as part of comprehensive sex hormone profiling alongside progesterone, testosterone, SHBG, DHEA-S, and LH/FSH for personalised hormone assessment in patients with fatigue, mood disturbance, libido changes, bone health concerns, or cardiovascular risk optimisation
Sample collection and turnaround
Sample type
Blood (serum)
Fasting required
No — fasting is not required for serum estradiol. However, collection timing relative to the menstrual cycle phase is the critical variable: for ovarian reserve assessment, collect on cycle day 2–3 (day 1 = first day of full flow); for ovulatory confirmation, collect at the expected mid-cycle peak; for corpus luteum and luteal phase adequacy, collect 7 days before the anticipated next menstruation (approximately day 21 of a 28-day cycle). For HRT monitoring, collect at a standard timing relative to dose — typically 24 hours after transdermal patch application or application of gel/spray for trough level; practitioners managing HRT should specify desired collection timing.
Collection method
Venipuncture at patient service centre
Turnaround
1–3 business days
Collection notes
Standard venipuncture into a serum separator tube (SST / gold top). Document on the requisition form: (1) menstrual cycle day and phase — mandatory for all premenopausal patients; (2) menopausal status and time since last menstrual period; (3) current oestrogen therapy — formulation (oral, transdermal patch, gel, spray, vaginal, implant, injectable), dose, and timing of most recent application relative to collection; (4) oral contraceptive use and formulation — OCP suppresses endogenous estradiol and results will reflect exogenous oestrogen; (5) fertility treatment context — natural cycle vs gonadotropin stimulation; (6) known haemoglobin variants or conditions affecting steroid assay performance; (7) relevant clinical context for male patients — gynaecomastia, hypogonadism, aromatase inhibitor therapy. # REVIEWER FLAG: Confirm LabCorp SST tube type, minimum serum volume, and any special handling requirements for the specific LabCorp estradiol test code. Confirm whether LabCorp offers both immunoassay and LC-MS/MS estradiol options under different test codes and clarify which code this listing corresponds to.
Specimen requirements
Minimum 0.5 mL serum. Centrifuge and separate serum within 2 hours of collection. Stable at 2–8°C for up to 7 days; stable frozen at −20°C for extended storage. Protect from prolonged light exposure — estradiol degrades with UV exposure over extended periods. # REVIEWER FLAG: Confirm minimum volume and stability data with LabCorp assay documentation for the specific test code.
What can affect Estradiol (E2) results?
Estradiol fluctuates by an order of magnitude across the menstrual cycle — from approximately 20–50 pg/mL in the early follicular phase through a mid-cycle peak of 200–400 pg/mL to 100–250 pg/mL in the luteal phase and near-zero at menstruation. A single estradiol result is uninterpretable without the cycle day and phase documented on the requisition form — the same numerical value of 60 pg/mL is consistent with early follicular adequacy, a blunted ovulatory peak, or elevated day-3 estradiol suggesting poor ovarian reserve, depending entirely on cycle timing. Cycle phase documentation is the single most critical pre-analytical contextual variable for this assay.
Oral oestrogen — in combined oral contraceptives and oral oestrogen HRT formulations — is absorbed from the gastrointestinal tract and undergoes extensive hepatic first-pass metabolism to oestrone (E1) and oestrone sulphate rather than remaining primarily as estradiol. Standard serum estradiol immunoassays may not fully capture the oestrogenic burden of oral oestrogen therapy — serum estradiol may appear low or mid-range despite substantial total oestrogenic exposure. Transdermal estradiol, by contrast, delivers estradiol directly to the systemic circulation without first-pass conversion, producing serum estradiol values that accurately reflect the delivered dose and making estradiol the appropriate pharmacokinetic monitoring marker for transdermal HRT. Oestrogen formulation and route must be documented on the requisition form.
Serum estradiol immunoassays measure total estradiol — the combined free and protein-bound fraction. Approximately 37% of circulating estradiol is bound to SHBG and 61% to albumin, with only approximately 2% circulating free. Elevated SHBG — from oestrogen therapy, thyroid hormone, or hepatic upregulation — reduces free estradiol bioavailability despite normal total estradiol concentration. Conversely, reduced SHBG from insulin resistance, androgens, or obesity increases free estradiol bioavailability. SHBG must be assessed alongside estradiol when bioavailable oestrogen rather than total oestrogen is the clinical question.
Adipose tissue expresses aromatase (CYP19A1) abundantly, converting circulating androgens — primarily androstenedione and testosterone — to oestrone and estradiol. In individuals with increased adipose mass, peripheral aromatisation produces supraphysiological oestrogen levels that suppress FSH and LH through negative feedback, contributing to anovulation, menstrual irregularity, and infertility in women, and to suppression of testicular testosterone production and gynaecomastia in men. BMI must be documented when interpreting estradiol in the context of fertility assessment or male hypogonadism.
LabCorp offers estradiol measurement by both immunoassay and liquid chromatography-tandem mass spectrometry (LC-MS/MS). At the low estradiol concentrations relevant to postmenopausal women, prepubertal children, and men, standard immunoassays systematically overestimate estradiol due to non-specific antibody cross-reactivity with other steroids — the Endocrine Society recommends LC-MS/MS as the preferred methodology for estradiol measurement at concentrations below approximately 50 pg/mL. At mid-range and high estradiol concentrations typical of premenopausal women, immunoassay and LC-MS/MS results are broadly comparable. Practitioners should confirm the LabCorp estradiol assay methodology for the relevant clinical context. # REVIEWER FLAG: Confirm which LabCorp test code applies to this listing and whether it uses immunoassay or LC-MS/MS, as this has direct implications for postmenopausal and male estradiol interpretation accuracy.
Significant haemolysis can interfere with steroid immunoassay optical density readings, potentially producing artefactually altered estradiol values depending on the degree of haemolysis and the specific assay platform. Estradiol is relatively stable in separated serum at refrigerator temperature but degrades with prolonged room temperature storage of whole blood before centrifugation. Specimens should be centrifuged and serum separated within 2 hours of collection and refrigerated promptly. # REVIEWER FLAG: Confirm LabCorp specimen rejection criteria for haemolysis for the specific estradiol assay code.
What do Estradiol (E2) results mean?
Elevated
Elevated estradiol above the cycle-phase-specific upper reference limit requires clinical context for interpretation. Elevated follicular-phase estradiol (day 2–3 >80 pg/mL) may reflect early follicular recruitment in diminished ovarian reserve — suppressing FSH below its true value and masking the FSH elevation that would reveal poor reserve; it may indicate a persistent luteal cyst from the prior cycle; or it may reflect exogenous oestrogen exposure. Elevated mid-cycle estradiol (>500–600 pg/mL) during ovulation induction indicates multifollicular response and OHSS risk. Elevated postmenopausal estradiol in the absence of HRT may indicate an oestrogen-secreting ovarian tumour, granulosa cell tumour, or — more commonly — peripheral aromatisation from obesity or exogenous oestrogen exposure. Elevated estradiol in males with gynaecomastia confirms oestrogen excess and warrants assessment of the aromatisation source — adiposity, liver disease, testicular tumour (Leydig cell), or oestrogen-secreting adrenal tumour. On HRT, estradiol above 200–250 pg/mL may indicate supra-physiological delivery and warrants dose reduction.
Normal
Estradiol within the cycle-phase-specific and age-appropriate reference range confirms adequate oestrogenic production from the indicated ovarian or peripheral source for that phase. In a symptomatic perimenopausal patient with hot flushes, sleep disturbance, and mood change, a technically normal but declining serial estradiol trend — fluctuating between 40 and 150 pg/mL with cycle-to-cycle variability — confirms early perimenopausal hormonal transition even when individual values remain within the reference range. A single in-range estradiol does not characterise the hormonal trajectory — serial measurements are required to map the perimenopausal decline. In HRT monitoring, an estradiol within the practitioner's target range (e.g., 50–150 pg/mL) alongside resolution of vasomotor symptoms confirms adequate therapeutic delivery.
Reduced
Low estradiol below the phase-specific lower reference limit indicates inadequate oestrogenic production. Persistently low early-follicular estradiol (<20–30 pg/mL) in a premenopausal woman with oligo-amenorrhoea suggests hypothalamic or pituitary suppression (hypothalamic amenorrhoea from energy deficit, excessive exercise, or psychological stress) or primary ovarian insufficiency — concurrent FSH, LH, AMH, and prolactin measurement distinguishes these. Postmenopausal estradiol below 10–15 pg/mL is expected in the absence of HRT and confirms natural oestrogenic quiescence. On HRT, estradiol below 40–50 pg/mL may indicate subtherapeutic delivery (poor transdermal absorption, incorrect site application, or inadequate dose) with persistent vasomotor and bone loss symptoms. Low luteal-phase estradiol below 50 pg/mL alongside low progesterone suggests an anovulatory cycle or inadequate corpus luteum function.
Note: The most clinically impactful caveat is the absolute requirement for cycle phase documentation — estradiol is meaningless without concurrent cycle day and phase information for premenopausal women. The second major caveat is the immunoassay vs LC-MS/MS platform difference at low concentrations: postmenopausal and male estradiol values below approximately 50 pg/mL are systematically overestimated by immunoassay, making LC-MS/MS the preferred methodology in these populations; practitioners should confirm the LabCorp test code methodology before interpreting results in these groups. The third caveat is oral vs transdermal oestrogen delivery context — serum estradiol is a reliable pharmacokinetic monitoring marker for transdermal oestrogen but less informative for oral oestrogen preparations where first-pass hepatic conversion to oestrone predominates and serum estradiol does not fully capture total oestrogenic exposure.
Frequently asked questions
The estradiol serum test measures 17β-estradiol — the most potent and biologically active endogenous oestrogen — in serum. It quantifies oestrogenic status from ovarian follicular production in premenopausal women, peripheral adipose aromatisation in postmenopausal women, or exogenous oestrogen from HRT or oral contraceptives. Because estradiol fluctuates dramatically across the menstrual cycle, results are only interpretable when the cycle day and phase are documented alongside the result.
How to access the Estradiol (E2) test
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Published: May 24, 2026
Last reviewed: May 24, 2026
- Stanczyk FZ, et al. Standardization of steroid hormone assays: why, how, and when? Cancer Epidemiol Biomarkers Prev. (2007)
- Santen RJ, et al. Postmenopausal hormone therapy: an Endocrine Society scientific statement. J Clin Endocrinol Metab. (2010)
- Practice Committee of the American Society for Reproductive Medicine. Testing and interpreting measures of ovarian reserve. Fertil Steril. (2012)
- Rosner W, et al. Position statement: Utility, limitations, and pitfalls in measuring testosterone: an Endocrine Society position statement. J Clin Endocrinol Metab. (2007)
This content is for licensed healthcare practitioners only and does not constitute medical advice. Clinical decisions should be based on the full clinical picture and not on any single test result.
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