FSH is the second pituitary gonadotropin, driving follicle growth and estradiol production in the ovary and supporting the Sertoli cells that sustain sperm production in the testis. The test reflects how strongly the pituitary is prompting the gonads. It speaks for the reproductive axis rather than for any single organ.
No readings for this marker yet.
Raised FSH most often means the gonad is responding poorly and negative feedback has weakened, as in menopause, primary ovarian insufficiency, or impaired spermatogenesis and primary testicular failure. Lowered FSH points more often to hypothalamic or pituitary under-signalling, seen with pituitary disorders, high prolactin, marked weight loss, endurance training or exogenous sex steroids. Because feedback normally moves it against the gonads' own output, it is informative mainly next to a sex hormone measured at the same time, which separates a high gonadotropin with a low steroid from a picture where both sit low. A single value out of range calls for a repeat and a doctor's reading.
In women the number is interpretable only with the cycle day, conventionally sampled in the early follicular phase, and it rises steeply after menopause. Hormonal contraception, recent illness and biotin supplements taken close to sampling can distort it. It is read together with LH and with estradiol or testosterone, and with prolactin when both gonadotropins sit low.
Reference ranges are general adult values and depend on lab, assay, age and sex. For orientation, not diagnosis — discuss results with your doctor.