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Free Androgen Index (FAI)
Specialistalso —
What it isA calculated estimate of free testosterone derived from total testosterone divided by SHBG and multiplied by 100.
DoesApproximates the free testosterone fraction when direct measurement isn't available.
GoodA high FAI in men signals strong functional androgen action.
BadA low FAI in men signals functional hypogonadism. In women, a high FAI signals androgen excess (PCOS, hirsutism).
- Standard
- Men >35%; women <8%.
- Optimal
- 55–90% men, 1–4% women (narrow target)
- Modifiers
- SHBG dominates the calculation.
How to optimize
- Lifestyle
- Same as free testosterone.
- Diet
- Same as free testosterone.
- Supplements
- Same as free testosterone.
- Peptides
- —
- Drugs
- Same as testosterone.
Reference ranges are general adult lab norms; optimal ranges are editorial picks from the longevity literature — not medical advice. Always interpret results with your physician.
within Men's Hormones