FSH

What it measures, and what changes the number.

FSH, follicle stimulating hormone, is made by the pituitary gland. It stimulates the development of ovarian follicles in women and supports sperm production in men. The test measures FSH in serum by immunoassay.

It is nearly always read with LH, the other pituitary hormone controlling the gonads, and with the hormones they regulate: estradiol and progesterone in women, testosterone in men. Prolactin is often added because it influences the same axis.

FSH varies across the menstrual cycle, so labs and clinicians often specify a particular cycle day for collection. It is also released in pulses, and hormonal contraception or other hormone treatments change it. Different immunoassays can give somewhat different results. Labs may print it as Hormona Folículoestimulante (FSH).

Reference ranges labs publish

Each lab states an interval for its own method and the population it measured. They differ, they are not interchangeable, and none of them is a verdict on a single result.

Often read alongside: LH, Estradiol (E2), Progesterone, Total testosterone, Prolactin

Blood test glossary