Estrone (E1): Which Tests to Order Alongside

Why Estrone Cannot Stand Alone

A single estrone value is like reading one sentence from a lab report and calling it a diagnosis. E1 reflects peripheral aromatization of adrenal androgens in fat tissue, but it says nothing about receptor-active estradiol levels, hypothalamic feedback status, or how the liver is clearing estrogen metabolites. The Endocrine Society's 2019 clinical practice guideline on menopause management recommends measuring multiple estrogen fractions alongside gonadotropins when evaluating postmenopausal hormone status.

Ordering estrone without estradiol misses the E1:E2 ratio, a clinically relevant metric. In premenopausal women, E2 dominates (E1:E2 ratio roughly 1:1 to 1:2). After menopause, this ratio inverts. E1 may exceed E2 by three- to fivefold. That shift matters because E1 is a weaker estrogen receptor agonist than E2, yet it serves as a reservoir. Sulfotransferases convert E1 to estrone sulfate (E1S), the most abundant circulating estrogen by mass, which tissues can reactivate locally via steroid sulfatase. Without measuring E2 and ideally E1S, the clinical picture stays incomplete.

Dr. Nanette Santoro, Professor of Obstetrics and Gynecology at the University of Colorado School of Medicine, has noted: "Estrone is the workhorse estrogen of the postmenopausal years, but interpreting it requires context from gonadotropins, binding proteins, and the patient's adiposity."

The Core Panel: E2, FSH, and SHBG

Start every estrone order with three companions. Estradiol (E2) quantifies the biologically most potent estrogen. FSH confirms menopausal status and hypothalamic-pituitary-gonadal axis integrity. Sex hormone-binding globulin (SHBG) determines how much estrogen is protein-bound versus free and bioavailable.

FSH above 30 mIU/mL on two draws spaced four to six weeks apart confirms menopause per the Endocrine Society's staging criteria. A postmenopausal woman with elevated E1 but suppressed FSH raises concern for an estrogen-secreting tumor (granulosa cell tumors produce E2 preferentially, but mixed tumors exist). Without FSH, that red flag goes undetected.

SHBG adds another layer. Produced in the liver, SHBG binds estradiol with high affinity and estrone with lower affinity. Low SHBG (common in obesity, insulin resistance, and hypothyroidism) increases free estrogen exposure to tissues even when total E1 appears normal. The 2020 AACE/ACE guidelines on postmenopausal hormone therapy emphasize SHBG measurement for women with metabolic syndrome receiving HRT, because low SHBG amplifies estrogenic effects beyond what total hormone levels predict.

A practical ordering framework: for any patient where you order E1, always add E2, FSH, and SHBG. Consider this the "estrone floor." Everything else builds on top based on clinical indication.

Estrogen Metabolite Testing: The 2:16 Ratio

Estrone is metabolized through three primary hydroxylation pathways in the liver. The 2-hydroxylation pathway (via CYP1A1/CYP1A2) produces 2-hydroxyestrone (2-OHE1), considered weakly estrogenic and potentially anti-proliferative. The 16α-hydroxylation pathway produces 16α-hydroxyestrone (16α-OHE1), which binds covalently to estrogen receptors and has genotoxic properties. The 4-hydroxylation pathway (CYP1B1) generates 4-hydroxyestrone, which can form DNA-damaging quinones.

The ratio of 2-OHE1 to 16α-OHE1 appears in the literature as a potential marker for estrogen-related cancer risk. A prospective study published in the Journal of the National Cancer Institute (N=10,786) found that women with a 2:16 ratio below 2.0 had measurably higher breast cancer incidence over 5.5 years of follow-up, though the absolute risk difference was modest.

This test is not standard. Order it when clinical context demands it: strong family history of ER-positive breast cancer, BRCA1/2 carriers, women on long-term estrogen therapy, or patients with persistently elevated E1 despite normal E2. The DUTCH (Dried Urine Test for Comprehensive Hormones) panel captures these metabolites alongside parent hormones. Quest and Labcorp offer serum 2-OHE1 and 16α-OHE1 as individual analytes.

A word of caution. The clinical utility of the 2:16 ratio remains debated. The WHI Observational Study did not find a statistically significant association between urinary estrogen metabolites and breast cancer risk after adjusting for BMI. Order this panel for risk stratification, not diagnosis.

DHEA-S and Androstenedione: Tracing the Upstream Supply

Estrone does not appear from nothing. It originates from androstenedione, which itself derives from DHEA and DHEA-S via the adrenal pathway. In postmenopausal women, the adrenals supply the androgen precursors that adipose aromatase converts to E1.

Measuring DHEA-S reveals whether the adrenal contribution is typical for age. DHEA-S declines roughly 2% to 3% per year after age 30. A postmenopausal woman with elevated E1 and a DHEA-S of 400 μg/dL (high for age 60, where the median is approximately 60 to 120 μg/dL) may have adrenal hyperactivity or an adrenal adenoma. A woman with elevated E1 and low DHEA-S points toward peripheral aromatization from excess adipose tissue as the primary source.

Androstenedione itself can be measured directly. Pairing it with E1 gives you the substrate-to-product ratio for aromatase activity. An E1/androstenedione ratio that is disproportionately high suggests increased aromatase expression, often seen in obesity (BMI ≥30 increases aromatase activity by an estimated 2- to 4-fold compared to normal weight).

Liver and Metabolic Panels: The Clearance Side

Estrone clearance depends on hepatic conjugation (sulfation, glucuronidation) and biliary excretion. Impaired liver function slows estrogen metabolism and raises circulating levels. A comprehensive metabolic panel (CMP) with ALT, AST, and albumin screens for hepatic dysfunction that could inflate E1 readings.

Add a lipid panel for HRT patients. Oral estrogen therapy increases hepatic SHBG production and can raise triglycerides by 15% to 25%, per a meta-analysis of 28 RCTs in the Cochrane Database. Transdermal estrogen avoids this first-pass effect. Tracking lipids alongside E1 helps clinicians decide between oral and transdermal routes.

Thyroid function (TSH, free T4) also interacts with estrogen binding. Hypothyroidism lowers SHBG, increasing free estrogen. Hyperthyroidism raises SHBG, potentially masking tissue-level estrogen effects. The American Thyroid Association recommends TSH screening in symptomatic women over 35, and pairing thyroid function with a hormone panel is efficient.

Fasting insulin and hemoglobin A1c round out the metabolic picture. Insulin resistance drives SHBG down and increases adipose aromatase activity, creating a feedback loop that sustains elevated E1. In the Nurses' Health Study (N=18,521 postmenopausal women), those in the highest quartile of fasting insulin had E1 levels 22% higher than those in the lowest quartile after adjusting for BMI.

Vitamin D and Bone Density Markers

Estrone plays a modest role in bone maintenance after menopause. While estradiol is the primary estrogen protecting against bone resorption, E1 contributes through local conversion to E2 in bone tissue via 17β-hydroxysteroid dehydrogenase. The AACE 2020 guidelines for postmenopausal osteoporosis recommend measuring 25-hydroxyvitamin D, calcium, and bone turnover markers (CTx, P1NP) alongside hormone panels in women at fracture risk.

A 25(OH)D level below 30 ng/mL is common in postmenopausal women. Combined with declining estrogen, this creates additive bone loss. Ordering vitamin D with E1 ensures you catch both contributing factors. If E1 and E2 are both low, bone turnover markers help determine whether bone loss is already active or merely a future risk.

How to Interpret the Results Together

Isolated numbers mislead. Patterns tell the story.

Postmenopausal baseline (no HRT): Expect E1 of 10 to 60 pg/mL, E2 below 20 pg/mL (LC-MS/MS), FSH above 30 mIU/mL. If E1 is above 60 with BMI above 30, suspect aromatase-driven excess. Check fasting insulin and DHEA-S.

HRT monitoring (oral estradiol): Oral estrogen undergoes first-pass hepatic metabolism, producing significant E1 from E2 conversion. The E1:E2 ratio on oral therapy often reaches 3:1 to 5:1. If E1 exceeds 150 pg/mL, consider dose reduction or transdermal switch. Per a 2017 position statement from The North American Menopause Society, target the lowest effective dose that controls symptoms.

Transdermal estradiol therapy: Bypasses the liver. E1:E2 ratio stays closer to 1:1. If E1 rises disproportionately on transdermal therapy, investigate adipose aromatization or exogenous E1 exposure (some compounded creams contain estriol/estrone blends).

Unexpectedly high E1 in a lean postmenopausal woman: Order adrenal androgens (DHEA-S, androstenedione), pelvic ultrasound, and consider CT adrenals. Rule out ovarian or adrenal estrogen-secreting tumors.

How to Lower Estrone (E1)

Excess E1 is typically an aromatase problem. Body fat reduction is the most effective intervention. A 10% reduction in body weight decreases circulating estrone by approximately 20% in obese postmenopausal women. Aromatase inhibitors (letrozole 2.5 mg daily, anastrozole 1 mg daily) are used in breast cancer treatment but are not indicated solely for lowering E1 in healthy women. Cruciferous vegetables (broccoli, cauliflower, Brussels sprouts) contain indole-3-carbinol, which shifts estrogen metabolism toward the 2-hydroxylation pathway. A randomized controlled trial (N=57) found that 400 mg/day of indole-3-carbinol significantly increased the 2:16 ratio.

Reducing alcohol intake matters. Alcohol inhibits hepatic estrogen conjugation. Women consuming more than one drink per day have E1 levels 10% to 15% higher than abstainers, per data from the European Prospective Investigation into Cancer and Nutrition (EPIC) cohort.

How to Raise Estrone (E1)

Low E1 is less commonly a primary clinical target. If both E1 and E2 are deficient and the patient is symptomatic (vasomotor symptoms, urogenital atrophy, bone loss), estrogen replacement therapy raises all estrogen fractions. Oral estradiol specifically raises E1 through hepatic first-pass conversion. For patients who need E1 preferentially (rare), compounded estrone creams exist but lack FDA-approved formulations and carry the same risks as any bioidentical estrogen product.

DHEA supplementation (25 to 50 mg daily) raises E1 indirectly by providing more androstenedione substrate for peripheral aromatization. A 12-month RCT of DHEA 50 mg/day in postmenopausal women (N=57) showed a significant increase in serum E1 and E2 alongside improvements in bone mineral density.

Specimen Collection and Practical Tips

Draw estrone as a fasting morning sample (7:00 to 9:00 AM). E1 has mild diurnal variation, though less pronounced than cortisol. Fasting minimizes postprandial SHBG fluctuations that could affect free estrogen calculations.

Specify LC-MS/MS (liquid chromatography-tandem mass spectrometry) rather than immunoassay when ordering. Immunoassays cross-react with estrone sulfate and other estrogen metabolites, inflating results by 15% to 30% in postmenopausal ranges where accuracy matters most. The Endocrine Society's 2010 position statement on hormone assays explicitly recommends mass spectrometry for low-concentration sex steroid measurements.

For women on transdermal estradiol, avoid applying the patch to the arm used for the blood draw. Skin contamination can produce falsely elevated E2 readings, which distorts the E1:E2 ratio interpretation. Allow 12 to 24 hours after the last patch application for a trough-level draw.