FSH and estradiol: what blood tests do and don't tell you

Summary

"Let me have a hormone test and find out whether I'm in menopause." It sounds sensible, but it conflicts with the nature of perimenopause: hormones fluctuate so much from day to day in this period that a single measurement is a photograph of that day, not a map of the stage. That is why guidelines find hormone testing unnecessary in women over 45 with typical symptoms; the stage is determined by your cycle pattern and your symptoms. Tests are genuinely valuable in particular situations: under 40, where things are unclear between 40 and 45, in decisions about contraception, and in ruling out causes other than menopause. Only your doctor interprets the results, together with your history.

What is happening?

The tests most often requested, and what each one tells you:

• FSH (follicle-stimulating hormone): A measure of the effort the brain is putting into stimulating the ovaries. It rises as the ovarian response declines. It is permanently high after menopause; in perimenopause it swings between high and normal even within the same month. A "normal" FSH does not mean you are not in perimenopause.

• Estradiol: The main estrogen. In perimenopause, rather than being low, it is erratic and at times high; after menopause it is low. At low levels the measurement precision of the laboratory is limited; small differences may not be meaningful.

• AMH (anti-Müllerian hormone): Reflects the remaining egg reserve; it is independent of the day of the cycle. It can estimate how close menopause is on a scale of years; it does not indicate symptoms or the need for treatment.

• LH: Accompanies FSH; on its own it adds no information.

• TSH (thyroid): Not a menopause test; but because thyroid disease mimics menopausal symptoms it is often requested — and should be.

• Blood count and ferritin: Show iron deficiency where bleeding is heavy.

What do we know?

• No test is needed over 45: NICE recommends identifying perimenopause by typical symptoms over the age of 45, and menopause by 12 months without a period, without testing; FSH measurement is not routinely requested in this group ¹.

• It can be considered between 40 and 45: Where there are symptoms and the diagnosis is unclear, FSH may help; but a single measurement is not relied on, and it may need repeating ¹.

• It is necessary under 40: In women under 40 whose periods become less frequent or stop, premature ovarian insufficiency (POI) is investigated; under the current international guideline (2024) the diagnosis can be made with a single raised FSH measurement alongside at least 4 months of irregular or absent periods; where the result is unclear, a repeat measurement and/or AMH is requested after 4-6 weeks and further investigations are done. POI is a distinct picture that requires HRT regardless of symptoms ⁵.

• The fluctuation is proven: In SWAN, FSH and estradiol showed large variability from month to month within the same woman; a lasting change became clear only as the final period approached. That is why STRAW+10 takes the cycle pattern, not hormone values, as the main criterion for staging; FSH is only a "supportive" criterion ^{3 2}.

• Hormonal contraception masks the results: In women taking a combined pill, FSH and estradiol measurements do not show perimenopause; with progestogen-only methods, FSH over the age of 50 can be used to help decide when contraception can be stopped ⁴.

• AMH roughly predicts the timing of menopause: A very low AMH indicates the final period is near; but the uncertainty of an individual prediction is high and routine use is not recommended ⁶.

• Saliva and hair hormone tests are not valid: These tests have no scientific validity in assessing menopause or in dosing treatment; guidelines do not recommend them ¹.

What does this give you?

• Set your expectations: If you are over 45 and your symptoms are typical, your doctor not requesting a test is not neglect — it is following the guideline. A test is not a precondition for treating your symptoms.

• Don't read a result on its own: Conclusions such as "my FSH came back at 8, so I've got a way to go" or "my FSH is 35, so it's definitely menopause" can be misleading in perimenopause. A result means something alongside your age, your cycle pattern, your symptoms and a repeat measurement.

• Ask for the right test: If you have fatigue, palpitations, weight change or hair loss, thyroid tests, a blood count, ferritin and vitamin D are usually more informative than FSH.

• Decisions about contraception: The assumption "I can't get pregnant any more" should not be made without testing; your doctor determines which method can be stopped and when.

Sources

1. NICE. Menopause: identification and management (NG23). 2015; updated November 2024.
2. Harlow SD, et al. Executive summary of the Stages of Reproductive Aging Workshop + 10. Menopause. 2012;19(4):387-395.
3. Randolph JF, et al. Change in follicle-stimulating hormone and estradiol across the menopausal transition. J Clin Endocrinol Metab. 2011;96(3):746-754.
4. Faculty of Sexual and Reproductive Healthcare. Contraception for Women Aged over 40 Years. 2017; updated 2023.
5. ESHRE/ASRM/CREWHIRL/IMS Guideline Group on POI. Evidence-based guideline: premature ovarian insufficiency. Climacteric. 2024;27(6):510-520.
6. Finkelstein JS, et al. Antimullerian hormone and impending menopause in late reproductive age. J Clin Endocrinol Metab. 2020;105(4):e1862-e1871.

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