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Free Androgen Index


The free androgen index (FAI) is a calculation used to determine the amount of testosterone which is free (unbound) in the bloodstream. Most testosterone is bound to proteins sex hormone binding globulin and albumin and is not available to interact with the body's cells. The FAI is a calculation based on the ratio of testosterone and SHBG and is a measure of the amount of testosterone that is available to act on the body's tissues.

The free androgen index is used in women to assess the likelihood of polycystic ovarian syndrome. In men, free testosterone gives a better indication of testosterone status.

What might a low result mean?

A low free androgen index could be a sign of lower than expected testosterone levels (androgen insufficiency). This can cause symptoms such as loss of libido, fatigue, and may also have an effect upon muscle and bone health. In men it can also cause problems with erectile dysfunction.

What might a high result mean?

An increased free androgen index is a sign of excessive testosterone. In women this is most commonly caused by polycystic ovarian syndrome (PCOS). Symptoms of PCOS can include irregular periods, the development of male characteristics such as unwanted hair, and acne.