Estrone Test · Blood

If you are a postmenopausal woman, estrone is the estrogen your body is actually making. Estradiol, the form most doctors test, drops so low after menopause that it often falls below what the lab can reliably measure. Estrone stays detectable and keeps working, quietly influencing breast cancer risk, bone health, body composition, and how you respond to hormone therapy. Knowing your estrone level gives you a window into your real estrogen status that a standard estradiol test frequently misses.

Estrone also reflects something standard hormone panels do not capture: how much estrogen your fat tissue is manufacturing on its own. Because fat cells convert other hormones into estrone through an enzyme called aromatase, your estrone level is a direct readout of this process. That connection between body fat and estrogen production is one of the key pathways linking obesity to postmenopausal breast cancer.

What Estrone Is and Where It Comes From

Estrone (E1) is one of three main estrogens your body makes, alongside estradiol (E2) and estriol (E3). All three belong to a family of hormones built from cholesterol. Estrone is structurally almost identical to estradiol but about 4 to 10 times weaker at activating estrogen receptors, the docking sites on cells that respond to estrogen. Your body freely converts estrone into estradiol and back again, so estrone acts as both a hormone on its own and a reservoir that tissues can tap when they need more estradiol locally.

Before menopause, your ovaries produce most of your estrogen, and estradiol is the dominant form. After menopause, ovarian production drops sharply. Estrone takes over as the main circulating estrogen, made primarily by aromatase in fat tissue converting an adrenal hormone called androstenedione. This shift means your estrone level after menopause is driven heavily by how much fat tissue you carry and how active that aromatase enzyme is.

Estrone also circulates in a storage form called estrone sulfate (E1S), which is the most abundant estrogen compound in your blood. Tissues throughout the body can take up estrone sulfate, strip off the sulfate group, and convert it back to active estrone or estradiol. This creates a whole-body distribution network for estrogen that operates even when your ovaries are no longer contributing.

Breast Cancer Risk

The link between estrone and breast cancer in postmenopausal women is one of the most consistently replicated findings in cancer epidemiology. Higher circulating estrone means more estrogen exposure to breast tissue, and that exposure fuels the growth of cancers that carry estrogen-responsive proteins on their surface (called hormone receptor-positive tumors).

A pooled analysis of eight prospective studies including 624 breast cancer cases and 1,669 controls found that the association between body mass index (BMI) and breast cancer risk was almost entirely explained by higher estrogen levels, including estrone and estrone sulfate. When estrogen concentrations were statistically accounted for, the excess risk from higher BMI essentially disappeared.

Sources: Baglietto et al. 2010 (Melbourne Collaborative Cohort); Adly et al. 2006 (Michigan case-control); Brantley et al. 2024 (Nurses' Health Study).

What this means for you: if you are postmenopausal, knowing your estrone level gives you a concrete data point about one of the strongest modifiable drivers of breast cancer risk. Women with estrone in the upper range have roughly two to three times the risk of those in the lower range. That is a large enough difference to motivate action, particularly since weight loss has been shown to bring estrone down.

Endometrial Cancer

The same estrogen exposure that raises breast cancer risk also applies to the uterine lining. In a nested case-control study within the Women's Health Initiative (WHI) involving over 93,000 postmenopausal women, higher levels of estrogens (particularly unconjugated estradiol, which interconverts with estrone) were linked to increased endometrial cancer risk. The effect of obesity on endometrial cancer was partially explained by these elevated estrogen levels. Estrone's role here follows from its position as the main circulating estrogen after menopause: higher estrone means more estrogen stimulation of the endometrium.

Estrone and Hormone Therapy

If you take estrogen therapy, the route of administration dramatically changes your estrone level. Oral estradiol passes through the liver before reaching your bloodstream. During that first pass through the liver, much of the estradiol is converted to estrone. In a study of 212 transgender women, oral estradiol produced roughly 8 to 10 times higher estrone levels compared to transdermal (patch or gel) estradiol. Transdermal delivery bypasses the liver, keeping the ratio of estradiol to estrone closer to what the body naturally produces.

This matters because the high estrone levels from oral estrogen have been associated with increased thrombin generation (a step in the blood clotting cascade), potentially explaining why oral estrogen therapy carries a higher blood clot risk than transdermal formulations. If you are on hormone therapy and tracking your estrone, a very high reading may reflect the liver's heavy conversion of oral estrogen rather than a problem with your body's own estrogen production.

Reference Ranges

Estrone reference ranges depend on your age, sex, menopausal status, and BMI. The values below come from a study of over 4,000 healthy postmenopausal women measured using a highly accurate lab technique called LC-MS/MS, which separates and identifies hormones with much greater precision than older methods. Your lab may use a different method and report slightly different numbers, so always compare results within the same lab over time.

Source: Richardson et al. (MAP.3 trial cohort, LC-MS/MS). Compare your results within the same lab over time for the most meaningful trend.

For premenopausal women, estrone varies with your menstrual cycle and is generally interpreted alongside estradiol. Modern LC-MS/MS reference ranges covering infancy through adulthood, stratified by sex and pubertal stage, have been published by Frederiksen et al. using Danish cohorts. These use units of pmol/L rather than pg/mL, so ask your lab which unit they report.

When Results Can Be Misleading

The single biggest confounder for estrone is exogenous hormones. If you are taking any form of estrogen therapy, oral contraceptives, or hormone replacement, your estrone result reflects the medication far more than your body's own production. One study found that a combined oral contraceptive containing estradiol valerate increased estrone roughly 13-fold. You cannot meaningfully interpret an endogenous estrone level while taking these medications.

• Oral estrogen therapy: Raises estrone dramatically through liver conversion. Transdermal estrogen has a much smaller effect on estrone. If you recently switched routes, wait at least 4 to 6 weeks before retesting.
• Body weight changes: Because fat tissue produces estrone, rapid weight gain or loss can shift your level. Test during a period of stable weight for the most interpretable result.
• Assay method: Older immunoassay methods have analytical variability of about 8 to 13% at low concentrations. LC-MS/MS is more accurate, especially for postmenopausal levels. Ask your lab which method they use.
• Recent illness or stress: Estrone may rise during serious illness alongside cortisol, reflecting a stress-driven shift in hormone production. Wait until you have fully recovered before testing.

Tracking Your Trend

A single estrone reading tells you where you are today, but a trend over time is far more useful. In postmenopausal women, estrone shows reasonable stability over weeks, with a 4-week reproducibility correlation of about 0.72. That means some natural fluctuation exists, and a modest change between two draws may simply reflect normal variation rather than a real shift in your estrogen status.

If you are making changes that could affect estrone, such as losing weight or adjusting hormone therapy, get a baseline, then retest in 3 to 6 months to see if the trend is moving in the direction you expect. After that, annual monitoring is reasonable for most people. If you are tracking the effect of weight loss specifically, the Campbell et al. trial showed measurable estrone reductions within 12 months of sustained caloric restriction, so give the intervention enough time before expecting to see a change on your labs.

Always retest through the same lab using the same method. Switching labs or methods can produce apparent changes that are really just differences in how the test is run.

What to Do With an Abnormal Result

If your estrone is higher than expected for your age and menopausal status, the first step is to rule out confounders. Are you taking any form of estrogen? Did you test during a stable weight period? Was the method reliable at low concentrations?

If the result is genuinely elevated, consider ordering estradiol (ideally by LC-MS/MS), SHBG (sex hormone-binding globulin, a protein that binds estrogen and reduces its activity), and FSH (follicle-stimulating hormone, which helps confirm menopausal status) to build the full picture. For women concerned about breast cancer risk, this hormone panel alongside BMI and family history gives a much more complete assessment than any single marker.

A persistently elevated estrone in a postmenopausal woman, especially combined with low SHBG and high BMI, describes a hormone profile consistently associated with increased breast and endometrial cancer risk. That pattern is not a diagnosis, but it is a signal to discuss screening frequency, weight management, and possibly referral to an endocrinologist or gynecologic oncologist. For women already diagnosed with hormone receptor-positive breast cancer, estrone is part of the monitoring picture when evaluating whether aromatase inhibitor therapy is adequately suppressing estrogen production.