Free Androgen Index Calculator
Calculate the Free Androgen Index from total testosterone and sex hormone-binding globulin (SHBG). Testosterone can be entered in ng/mL or nmol/L.
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What is the Free Androgen Index?
The Free Androgen Index (FAI) is a calculated ratio of total testosterone and sex hormone-binding globulin (SHBG). It is expressed as a percentage and can provide an estimate of the relative androgen availability.
FAI is particularly used in the evaluation of hyperandrogenism in women, including conditions such as polycystic ovary syndrome. It should be interpreted together with clinical findings and laboratory results.
FAI Reference Interpretation
| Patient group | Reference approach | Interpretation |
|---|---|---|
| Adult women | Example interval: 0.4 - 8.4 % | Use the laboratory-specific reference interval whenever available. |
| Adult men | Laboratory-specific | FAI is less commonly used as the primary androgen assessment in men. |
| Adolescents | Age- and puberty-specific | Adult reference intervals should not be applied automatically. |
Reference intervals are method-, population- and laboratory-dependent. The example female interval shown above should not replace the reference interval supplied by the performing laboratory.
Free Androgen Index Calculator - Frequently Asked Questions
What is the formula for FAI?
FAI is calculated as total testosterone in nmol/L divided by SHBG in nmol/L, multiplied by 100.
Can testosterone be entered in ng/mL?
Yes. The calculator automatically converts testosterone from ng/mL to nmol/L before calculating FAI.
How is testosterone converted?
Testosterone in ng/mL is multiplied by 3.467 to convert it approximately to nmol/L.
Why is SHBG important?
SHBG binds circulating sex hormones. Changes in SHBG can substantially alter the calculated FAI even when total testosterone remains unchanged.
Is FAI the same as free testosterone?
No. FAI is a calculated index and is not a direct measurement of free testosterone.
Can FAI diagnose PCOS?
No. FAI may support the assessment of biochemical hyperandrogenism, but PCOS diagnosis requires clinical assessment and appropriate diagnostic criteria.
Medical Disclaimer: This calculator is intended for educational and clinical reference purposes. The Free Androgen Index is a calculated parameter and should not be interpreted in isolation. Reference intervals vary according to laboratory method, assay characteristics, population, age and sex. Clinical interpretation should consider total testosterone, SHBG, symptoms, menstrual history and other relevant laboratory findings. This calculator does not replace professional medical evaluation.
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