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Free Androgen Index Interpretation

Meaning

The Free Androgen Index (FAI) is a calculated ratio, typically of total testosterone to sex hormone-binding globulin (SHBG), used clinically as a surrogate marker to estimate the biologically active, or “free,” fraction of androgens. Interpretation involves comparing this calculated value against established reference ranges, often to assess androgen status in conditions like hirsutism in women or hypogonadism in men. It provides a more nuanced view of androgen bioavailability than total testosterone alone, which includes the protein-bound, inactive fraction.