What it measures
- Testosterone
- SHBG (sex hormone binding globulin)
- Free androgen index (FAI)
Who it’s for
- Acne in adulthood
- Excess facial or body hair
- Irregular periods or suspected PCOS
- Thinning hair on your scalp
Why total testosterone isn’t the whole story
Most of the testosterone in your blood is bound to SHBG and can’t act on your body. The free androgen index compares your total testosterone with your SHBG to estimate the active part. Two women with the same testosterone can have very different FAIs if their SHBG differs, which is why both are measured.
Signs of high androgens
In women, raised androgens can cause adult acne, extra hair on the face, chest or tummy, thinning scalp hair and irregular periods. PCOS is the most common cause. Excess weight and insulin resistance lower SHBG, which raises FAI, so lifestyle changes can make a real difference.
How to prepare
- Morning appointments give the most reliable result.
- Stop biotin (vitamin B7) supplements, often found in hair, skin and nail products, 48 hours before.
- No fasting needed. Eat and drink as normal.
How it works at our Croydon clinic
Book online
Choose your test and a time that suits you. No GP referral needed.
A 15-minute visit
A trained clinician takes a small blood sample at 169 Shirley Road, Croydon. Tell us if you’re nervous.
Results in 1–3 days
A clear report showing each result against its reference range.
Next steps
Share your report with your GP, who can arrange NHS follow-up if anything needs it.
Questions
Is this test for women or men?
It’s mostly used for women with possible PCOS or signs of excess androgens. Men checking for low testosterone are usually better served by our Testosterone and SHBG tests.
Do I need to time it in my cycle?
Cycle timing matters less than for FSH and LH. A morning appointment gives the most reliable result.
How much is a Free Androgen Index in Croydon?
£85 at our clinic at 169 Shirley Road, Croydon, including taking your blood sample and your report.
How quickly will I get my results?
Usually within 1 to 3 days, in a clear report showing each result against its reference range.