The follicle-stimulating hormone (FSH) test is a blood test that measures the level of FSH in the body. FSH is a hormone produced by the pituitary gland that helps regulate the menstrual cycle and the production of eggs in women and sperm in men. In women, FSH stimulates the growth of ovarian follicles, which contain developing eggs. In men, FSH stimulates the production of sperm in the testicles. The FSH test is commonly used to evaluate fertility in both men and women. In women, the test can help diagnose conditions such as polycystic ovary syndrome (PCOS), premature ovarian failure, or menopause. In men, the test can help diagnose conditions such as Klinefelter syndrome or pituitary gland tumors. Abnormal levels of FSH can also indicate other conditions, such as thyroid dysfunction or adrenal gland dysfunction. The FSH test is a simple and relatively non-invasive procedure that involves drawing a blood sample from a vein.