What it measures
FSH (follicle stimulating hormone) is made by the pituitary gland at the base of the brain. In men it drives sperm production, and in women it drives the growth of eggs in the ovaries. The test measures how much is in the blood.
Why people test it
- Measured in fertility tests for both men and women.
- Used with LH and oestradiol when looking into the menopause or irregular or missed periods.
- Read with testosterone in men, to see whether low testosterone starts in the testes or the pituitary.
- TRT and anabolic steroids switch off the body's own FSH, so it reads low while they are in use.
- Checked after a steroid cycle to see whether the body's own hormone production has restarted.
Typical range
Ranges vary between labs, with the method used, age and sex, and your report shows the lab's own range. For men, one NHS trust lab gives 1.0 to 12.0 IU/L. For women the range depends on the stage of the menstrual cycle and is much higher after the menopause. Source: Oxford University Hospitals NHS Foundation Trust: biochemistry reference ranges.
Finger-prick or vein?
A vein draw is usually advised. FSH is often tested alongside testosterone or oestradiol, and gels or creams on the fingers can contaminate a finger-prick sample's hormone results.
In women who have periods, FSH changes through the cycle, so the day of the cycle the sample is taken affects the result.