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Immunology & Autoimmune
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Currently under review
Pending specialist review and validation.
Follicle stimulating hormone is a hormone made by your pituitary gland that helps control the reproductive system. In women, it supports the growth of ovarian follicles and the production of estrogen. In men, it acts on the testes to support sperm production.
This test measures the amount of follicle stimulating hormone in a blood sample. Levels naturally vary with age and life stage, and in women they also change across the menstrual cycle. Your clinician may look at this result together with other hormones, such as luteinizing hormone and estradiol, to understand how your reproductive system is functioning.
FSH testing helps evaluate fertility concerns, irregular or absent periods, menopausal status, and possible problems with the ovaries, testes, or pituitary gland. In men, it helps distinguish whether low testosterone or fertility problems are due to a testicular issue or a pituitary or hypothalamic cause. In children and adolescents, it can be used as part of an evaluation for early or delayed puberty.
Clinicians also use FSH to monitor response to certain fertility treatments and to help assess ovarian reserve along with other tests. The blood draw is a low-risk procedure, although timing of the test and medications can affect the result, so your clinician may recommend specific scheduling or repeat testing.
Interpreting your result depends on your age, sex, menstrual phase, pregnancy status, and any hormones or fertility medicines you take. Higher values can be seen when the ovaries or testes are not responding well, which can prompt the pituitary to signal more strongly. Lower values can occur when the pituitary or hypothalamus is underactive, or when hormones or medications are suppressing the normal signals.
Your clinician will usually consider FSH alongside other tests and your symptoms. For example, they may review luteinizing hormone, estradiol, anti-Müllerian hormone, inhibin B, or semen parameters, and may ask about cycle patterns or sexual development. If results are unexpected, your care team might suggest repeating the test at a specific time, adjusting medications, or doing additional imaging or referral to a specialist.
Reference intervals vary by laboratory, analyzer, methodology, population, and units. The ranges shown here are for education only. Always interpret your results against the reference interval printed on your own lab report.
In people who menstruate, FSH fluctuates across the cycle. Drawing blood in the early follicular phase is often preferred for consistency, so timing instructions from your clinician matter.
Birth control pills, patches, rings, progestins, and hormone therapy can suppress FSH. Always tell your clinician about all hormones you use so results are interpreted correctly.
Drugs such as clomiphene, letrozole, gonadotropins, and GnRH analogs can raise or lower FSH temporarily. Testing may be scheduled around treatment cycles to avoid misleading results.
During pregnancy and while breastfeeding, hormonal feedback often suppresses FSH. Your stage of pregnancy or postpartum status should be considered when interpreting results.
Tumors, prior surgery or radiation, trauma, or chronic systemic illness can affect pituitary signals and lower FSH. Your medical history helps guide interpretation.
High-dose biotin and some supplements can interfere with certain immunoassays. Avoid nonessential high-dose biotin before testing and tell your clinician what you take.
Significant stress, illness, or extreme exercise can alter reproductive hormone signaling. If you were unwell or training heavily, your clinician may recommend retesting.
FSH levels change with puberty and with the transition to menopause. Your age and developmental stage are essential context for interpreting a single measurement.
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