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Dr. Andrea Pinto Lopez

Sep 19, 20227 min read

What Does the Free Androgen Index Mean?

The information provided herein does not constitute an expert or medical advice, nor intended to replace such advice.


Your hormone levels are very important for your health, and your body is constantly working hard to keep these levels within a normal range. When your hormone levels become altered, it can lead to a wide variety of signs and symptoms, and it can even lead to serious health complications.

There are many tests that can be used to measure the levels of different hormones in your body. A calculation called free androgen index can be used to determine whether you have abnormal androgen levels. But why is this important, and who should get a free androgen index done? 

What is the free androgen index (FAI)?

The free androgen index or free testosterone index is used to determine whether your androgen levels are normal. According to the Cleveland Clinic, androgens are a group of sex hormones that help stimulate the process of puberty so that people mature physically. People of all genders produce androgens, but males have much higher androgen levels.

The main type of androgen is testosterone. Testosterone is produced by the testicles in males, and by the ovaries in females.

A free androgen index (FAI) is a ratio that is calculated after getting a blood testosterone test. According to the University of Rochester Medical Center, blood testosterone tests include different types of tests, such as:

  • Total testosterone
  • Free testosterone
  • Sex-hormone binding globulin (SHBG)

A FAI is used to compare the amount of total testosterone in your blood versus the amount of sex-hormone binding globulin (SHBG).

What does your free androgen index mean?

A large amount of your total testosterone is typically bound to SHBG. When testosterone is bound to SHBG, it can’t be used by your tissues. This is one of the methods that your body uses to regulate testosterone levels.

However, high or low SHBG levels can alter the levels of testosterone that your body can use. High SHBG can lead to symptoms of low testosterone, while low SHBG can lead to signs of high testosterone.

A FAI is calculated by dividing total testosterone by SHBG. According to the NHS, calculating a free androgen index is especially useful when total testosterone levels are normal, but they’re still accompanied by symptoms of high testosterone levels.

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FAI is only reported in females, and it can be useful to diagnose and monitor conditions such as polycystic ovarian syndrome (PCOS) and hirsutism (excessive facial and body hair), which are commonly associated with elevated testosterone production.

Other signs of high testosterone levels in women can include:

  • Acne
  • Oily and inflamed skin
  • Scalp hair loss
  • Irregular or absent periods
  • Infertility
  • Weight gain
  • High cholesterol

Over time, high testosterone in women can lead to complications such as type 2 diabetes and obesity.

Free androgen index calculator

In order to calculate your free androgen index, you need to have test results for total testosterone and SHBG levels. To calculate your FAI, you simply need to divide your total testosterone by SHBG results.

However, it’s important to keep in mind that these tests must be ordered by a healthcare professional, since they’re not part of routine testing. You must also discuss your results with your doctor, since they’ll be able to help you interpret their meaning and impact on your health.

You can learn more about many other reproductive health topics, including at-home STD testing, at STDWatch.com now.


Androgens - my.clevelandclinic.org

Free Androgen Index - urmc.rochester.edu

Test Directory / Free Androgen Index - yorkhospitals.nhs.uk

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