Free Androgen Index
Discover Free Androgen Index for hormone balance evaluation in women. Monitor androgen activity for reproductive health insights.
What is Free Androgen Index?
Free Androgen Index (FAI) is a calculated ratio of total testosterone to sex hormone binding globulin (SHBG), expressed as a percentage. It estimates the amount of biologically active testosterone by accounting for how much is bound to SHBG and therefore unavailable to tissues.
Why is it Tested?
Doctors order FAI to assess androgen activity when direct free testosterone measurement isn’t available or reliable. It’s particularly useful for evaluating PCOS, hirsutism, and other androgen-related conditions in women, and can help assess functional testosterone status in both sexes.
Normal Ranges
Reference ranges vary by lab and gender. General adult guidelines:
- Women: 1–10%
- Men: 30–150%
The calculation is: (Total Testosterone ÷ SHBG) × 100
Higher ratios indicate greater androgen activity.
Reference ranges vary by authority. Track yours across multiple standards with automatic unit conversions in LabsVault.
What do Abnormal Results Mean?
Abnormal results are not a diagnosis. Always discuss your results with a qualified healthcare provider before making any medical decisions.
Low FAI
Low values may indicate:
- Low testosterone production
- High SHBG levels
- Hypogonadism
- Age-related hormone decline
High FAI
Elevated FAI may suggest:
- PCOS (in women)
- Low SHBG levels
- Excessive androgen activity
- Insulin resistance or metabolic syndrome
How to Track Over Time
FAI provides a stable estimate of androgen activity that’s less affected by SHBG fluctuations than free testosterone alone. Tracking FAI over time helps monitor hormonal balance, treatment responses, and metabolic health changes that affect androgen availability.
Track your Free Androgen Index results over time
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