FSH (follicle stimulating hormone)

Women: 3.5 to 12.5 IU/L · Men: 1.5 to 12.4 IU/L

In women the range depends on the phase of the cycle (about 3.5 to 12.5 IU/L in the first half, higher at mid-cycle, 1.7 to 7.7 in the second half) and is much higher after the menopause (roughly 26 to 135), so the lab's phase-specific range matters.

FSH is a messenger hormone from the pituitary gland at the base of the brain. In women it drives the growth of egg follicles in the ovary each cycle; in men it supports sperm production in the testes. When the ovaries or testes slow down, the pituitary sends more FSH, so the level rises.

Doctors request it to look at irregular or absent periods, fertility, early menopause, and in men with low testosterone or fertility concerns. It is usually paired with LH, and in women the day of the cycle is recorded.

• The menopause and the years leading up to it
• Ovaries or testes that are working less well, from any cause
• The mid-cycle surge in women, briefly
• Some inherited conditions affecting the ovaries or testes
• Older age in men, in the general population

• The combined contraceptive pill, HRT and other hormone medicines
• Pregnancy
• Pituitary or hypothalamus problems, which are uncommon
• Low body weight, heavy exercise and eating disorders
• Anabolic steroid and testosterone use in men
• Some hormone treatments for prostate cancer and endometriosis

• The value depends heavily on the day of the cycle it was taken
• Hormonal contraception suppresses it
• A single mid-cycle value can look high without anything being wrong

In women it is usually taken between day 2 and day 5 of the cycle, counting the first day of bleeding as day 1, and the day should be noted. No fasting needed. In men a morning sample is preferred.

Written by a UK consultant physician. Typical UK adult reference ranges; your laboratory's own printed range takes precedence.