A patient brings me a lab report from another clinic. It says "estrogen: 142 pg/mL" with no further breakdown. She is 48, has been on a compounded estrogen cream for six months, and her hot flashes are slightly better but her sleep is worse and she has gained eight pounds in the abdomen. The lab does not tell me what I need to know. "Estrogen" is not one molecule — it is a category. There are three estrogens that circulate in measurable amounts in a woman's body, and they do meaningfully different things. A panel that lumps them together is the equivalent of measuring "blood cells" without distinguishing red from white.
This article walks through what each of the three estrogens actually does, why the distinction matters when you are evaluating symptoms or therapy, and what I order on a real hormone panel at the first visit.
The three estrogens — what each one does
Estradiol (E2). This is the dominant estrogen during the reproductive years. Produced primarily by the ovarian follicles, it is the most biologically potent of the three by a wide margin — roughly 10 times more potent at the estrogen receptor than estrone, and about 80 times more potent than estriol. When you read about estrogen's role in bone density, cardiovascular protection, brain function, mood regulation, sleep architecture, vaginal tissue health, and skin collagen — you are reading about estradiol. Almost everything we associate with the protective effects of estrogen is mediated by E2. In a healthy reproductive-age woman, serum estradiol fluctuates between roughly 30 pg/mL early in the follicular phase and 200-400 pg/mL at ovulation. In post-menopause, untreated, it drops to under 20 pg/mL and often into single digits.
Estrone (E1). This is the dominant estrogen after menopause. Once the ovaries stop producing meaningful estradiol, the body's estrogen production shifts to peripheral conversion of androgens (mostly androstenedione from the adrenal glands) into estrone in adipose tissue, the liver, and skin. Estrone is weaker at the estrogen receptor than estradiol, but it is the form that most post-menopausal women have circulating at the highest concentration. Critically, estrone can be back-converted to estradiol in some tissues, and there is a bidirectional relationship between the two — they interconvert via the 17β-HSD enzyme system. An elevated estrone level in a post-menopausal woman is often a marker of higher adipose tissue mass, because the conversion happens in fat. That has implications I will come back to.
Estriol (E3). This is the weakest estrogen. It is produced in significant amounts only during pregnancy, by the placenta. Outside of pregnancy, it circulates at very low levels — essentially clinically irrelevant in serum. Estriol is, however, a major component of compounded "Bi-Est" creams (typically 80 percent estriol, 20 percent estradiol) marketed under the premise that estriol provides "safer" estrogenic activity. The clinical reality is more nuanced. Estriol applied topically to vaginal tissue produces meaningful local effect because it binds estrogen receptors there efficiently. Systemic estriol from a transdermal preparation produces unpredictable serum levels and unclear systemic benefit, because most of it is rapidly cleared.
Why the distinction matters clinically
If a patient is being treated for vasomotor symptoms (hot flashes, night sweats) and her estradiol is still under 30 pg/mL, she is not adequately replaced — regardless of what her "total estrogen" reads. The receptors that mediate vasomotor stability respond to estradiol. Estriol does not effectively occupy them in a way that suppresses hot flashes.
If a patient has elevated estrone but low estradiol — common in post-menopausal women carrying excess adipose tissue — the picture is more complicated. The elevated estrone is not protective in the way estradiol would be. It can drive estrogen-receptor activity in tissues like breast and endometrium without providing the cardiovascular, bone, and cognitive benefits that estradiol does. This is part of why obesity is paradoxically associated with both lower estradiol and higher estrogen-driven cancer risk in post-menopausal women — the wrong estrogen, in the wrong tissue, in inadequate amounts.
If a patient is on a Bi-Est compound and her serum estradiol is barely measurable, she is essentially on placebo for the systemic indications. Vaginal symptoms may improve from local estriol effect; sleep, mood, bone, and cardiovascular benefits will not.
These are not theoretical distinctions. I see them in real lab work weekly.
The mechanism — why three forms exist at all
Estradiol is synthesized in the ovary from cholesterol via the steroidogenesis pathway: cholesterol to pregnenolone, to androstenedione, to testosterone, to estradiol via the aromatase enzyme. After menopause, when ovarian production fails, the same aromatase enzyme — present in adipose tissue, liver, and skin — converts adrenal androstenedione to estrone instead. Estrone is then partially converted to estradiol in peripheral tissues by 17β-HSD, but the conversion rate is not high enough to maintain protective estradiol levels in most women.
Estriol is a metabolite — produced primarily in pregnancy from placental estrogens, otherwise present at low levels as a downstream conversion product of estradiol and estrone via 16α-hydroxylation. Its physiological role outside of pregnancy is not entirely clear, and the case for supplementing it as a primary therapeutic estrogen has more historical and marketing weight than mechanistic weight.
The bottom line: in a non-pregnant woman, the relevant estrogens for hormonal therapy decisions are estradiol and estrone. Estriol has a defined role in vaginal therapy and a poorly defined role systemically.
What I look for on a real hormone panel
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When I evaluate a woman for hormone optimization, I do not order "total estrogen." I order a panel that lets me see the actual physiology:
- Estradiol (E2) — serum, sensitive assay if she is post-menopausal or on transdermal therapy. The standard immunoassay starts losing accuracy below 30 pg/mL. For perimenopausal monitoring, day-of-cycle matters — I either time the draw or interpret the value with the cycle context.
- Estrone (E1) — serum. Especially important post-menopausal, especially in patients with higher BMI.
- Progesterone — paired with estradiol, especially in perimenopause where estrogen-progesterone imbalance is often a bigger driver of symptoms than absolute deficiency of either.
- Total and free testosterone — both numbers, not just total. Testosterone deficiency is one of the most under-recognized contributors to mid-life symptoms in women.
- DHEA-S — adrenal androgen reserve. Affects downstream estrogen and testosterone production after menopause.
- SHBG — sex hormone binding globulin. Tells me what is actually bioavailable. A high SHBG can leave a woman symptomatic despite "normal" total hormone levels.
- FSH and LH — useful for confirming menopausal status and ruling out hypothalamic-pituitary issues.
- Full thyroid panel — TSH, free T3, free T4, reverse T3, antibodies. Thyroid dysfunction mimics and worsens estrogen deficiency symptoms; you cannot interpret one without the other.
- Metabolic markers — fasting insulin, HbA1c, lipid panel. Insulin resistance affects SHBG and aromatase activity directly.
Comprehensive lab work is the foundation. Without this picture, any conversation about which estrogen form, which dose, and which delivery route is informed guessing.
How I use the data to build the protocol
The decision tree, simplified:
If a woman is symptomatic, her estradiol is low, and she has no contraindications — bioidentical estradiol replacement, usually transdermal (patch, cream, or pellet), at a dose calibrated to symptom response and serum target. Oral estradiol exists but I rarely use it as first-line because the first-pass hepatic metabolism produces a different downstream estrone-to-estradiol ratio and increases SHBG and clotting factors compared to transdermal.
If she has a uterus, she gets progesterone alongside estrogen. Not optional. Bioidentical micronized progesterone, oral, dosed at bedtime, both for endometrial protection and for the GABAergic sleep benefit progesterone provides.
If her estrone is elevated relative to her estradiol — particularly in the setting of elevated BMI — addressing the metabolic and adipose contribution is part of the treatment plan, not a separate consideration. This is where the medical weight loss conversation often integrates with hormone therapy. Reducing visceral adipose tissue reduces aromatase activity and shifts the estrone-estradiol ratio toward something more physiologically favorable.
If her primary symptoms are vaginal — dryness, dyspareunia, recurrent UTIs — vaginal estriol or low-dose vaginal estradiol is the right tool. Local therapy, local effect, minimal systemic absorption, no need to commit to systemic hormone replacement to address a local problem.
If she wants pellet-based therapy and is a candidate, Biote pellet therapy provides a sustained-release option that some patients prefer over the discipline of daily or weekly applications. The pellet itself is bioidentical estradiol or testosterone, dosed by patient size and lab targets.
What I will not do
I will not write a prescription for estrogen without paired progesterone in a woman with a uterus. I have seen patients arrive on estrogen monotherapy from other clinics and I treat that as a finding to address before continuing.
I will not start hormone therapy on lab values from a panel that did not include the relevant markers. If a patient brings me labs that measured TSH and "total estrogen" only, we redraw with the full panel before we plan.
I will not chase a lab number without symptom correlation. The goal is not to optimize a number on a page; it is to relieve symptoms and provide the protective benefits estrogen mediates while staying within a safe range. The number is a guide, not the target.
The next step
If you have been on an estrogen product without ever seeing the full breakdown of which estrogen forms are circulating in your blood, the most useful thing you can do is request a panel that includes estradiol, estrone, progesterone, free testosterone, SHBG, and a full thyroid panel before your next refill. If your current provider will not order it, that itself is information about whether the relationship is the right one for the kind of care you are asking for.
You can request the full panel at either the Columbus or Warner Robins clinic — same labs, same protocols, same approach at both locations. Travis Woodley sees patients at both on a rotating schedule. Bring any prior labs and any prior prescription history to the first visit. We start with what is actually in your blood and build the plan from there.
Medical disclaimer: This article is for educational purposes only and does not constitute medical advice. Individual clinical decisions should be made in consultation with a qualified healthcare provider following appropriate evaluation. References to specific treatments, dosing, or protocols are informational.
Travis spent 17+ years in high-acuity clinical medicine — emergency, cardiac ICU, and cath lab — before founding Revitalize. He is a Certified Platinum Biote hormone therapy provider, the published author of You're Not Broken — You're Unbalanced, and the founder of the Rebuild Metabolic Health Institute. His clinical writing reflects the same precision he brought to critical care: specific, honest, and built around what actually works.
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