Free Androgen Index (FAI) Calculator

The Free Androgen Index (FAI) is a ratio used to estimate the amount of biologically active or free testosterone in the body. Testosterone, the primary male sex hormone, circulates in the blood in two main forms: bound to proteins, such as Sex Hormone-Binding Globulin (SHBG), and unbound or free.

The Free Androgen Index is calculated using the following formula:

FAI = (TT × 100) / SHBG

Where:

  • TT (Total Testosterone) is the total amount of testosterone in the blood.
  • SHBG (Sex Hormone-Binding Globulin) is a protein that binds to sex hormones, including testosterone.

Free Androgen Index reference values

Age Male Female
< 29 30.0 – 128.0 0.4 – 8.4
30 to 39 24.0 – 122.0

0.4 – 8.4

40 to 49 14.0 – 126.0 0.4 – 8.4
> 49 18.0 – 82.0 0.4 – 6.6

By calculating the Free Androgen Index, one can get an estimate of the proportion of total testosterone that is not bound to proteins and is therefore considered more biologically active.

It's important to note that while the Free Androgen Index provides an estimate, direct measurements of free testosterone levels through laboratory tests are considered more accurate. The Free Androgen Index is used in situations where direct measurement may not be feasible or cost-effective. Interpretation of the FAI should be done in consultation with a healthcare professional, as individual variations and other factors can influence the results.

Based on research by

Gender
years
ng/mL
  • nanomoles per liter (nmol/L)
  • nanograms per deciliter (ng/dL)
  • nanograms per milliliter (ng/mL)
nmol/L
Free Androgen Index (FAI)
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