What it measures
- Testosterone
- SHBG (sex hormone binding globulin)
- Free androgen index (FAI)
What is the free androgen index?
Women naturally make small amounts of testosterone. Much of it is bound to a protein called SHBG and isn’t active. The free androgen index (FAI) compares your total testosterone with your SHBG to estimate how much is free to act on your body.
A raised FAI is common in polycystic ovary syndrome and can explain acne, extra hair growth and irregular periods. For a full PCOS work-up, our PCOS Profile adds FSH, prolactin, DHEA-S, cortisol and AMH.
Who it’s for
- Acne in adulthood
- Excess facial or body hair
- Irregular periods or suspected PCOS
- Thinning scalp hair
How to prepare
- Drink plenty of water beforehand; it makes the sample quicker and easier to take.
- You don’t need to fast.
- Morning appointments give the most reliable result.
- Stop biotin (vitamin B7) supplements 48 hours before, as biotin can affect hormone and thyroid results.
Free Androgen Blood Test: your questions
Is this test for women or men?
It’s mainly used for women investigating symptoms of excess androgens, such as acne, hair growth or irregular periods. Men usually need a testosterone and SHBG test instead.
Information on this page is general and doesn’t replace advice from your GP, midwife or consultant. If you feel unwell or are worried about symptoms, contact your GP, call NHS 111 or, in an emergency, 999.