Summary

The Free Androgen Index (FAI) is a calculated ratio used to estimate the amount of free or unbound testosterone present in the bloodstream. This unbound testosterone is the fraction that is bioavailable and can exert its effects on the body. The FAI can provide valuable insight into conditions related to androgen levels.

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Overview

Testosterone is the primary male sex hormone, playing critical roles in both men's and women's bodies. It contributes to muscle mass, bone density, red blood cell production, and affects mood and libido. Most testosterone in the body is bound to proteins, namely sex hormone-binding globulin (SHBG) and albumin. The remaining fraction, which is unbound, represents the free testosterone available to tissues.

The Free Androgen Index (FAI) is a calculated ratio that estimates the proportion of free to total testosterone. Higher FAI values often indicate increased free testosterone levels and may suggest conditions like PCOS in women or a testosterone-secreting tumor. Conversely, lower FAI values might signify conditions such as hypogonadism in men, caused by problems in testes, pituitary, or hypothalamus.^[1,2]

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What should you know about this biomarker?

Laboratories employ different equipment and protocols, leading to variations in reference ranges or units of measurement. In Macromo blood tests, we use the unit of measure % (percentage).

The equation used for the calculation is written below: 

FAI index [%]= (Testosterone SHBG) * 100

Ideal levels vary between individuals and genders. Typically, FAI values between 10-110 % in males and 0.6-6 % in females are considered normal, depending on the lab. The values depend on factors such as the individual's age, sex, and overall health status.^[3,4]

There are three possible states of your blood test result: low, average, and high levels.

• Your Free Androgen Index is low, potentially indicating an underlying condition such as hypogonadism. Contact a healthcare provider to determine the root cause.
• Your Free Androgen Index is within the normal range. That indicates balanced hormonal activity. Keep a healthy lifestyle with regular exercise, balanced nutrition, and adequate sleep.
• Your Free Androgen Index is elevated. It means that your body might be producing excessive androgens. It can indicate a polycystic ovarian syndrome (PCOS) or a testosterone-secreting tumor. Consult this with a healthcare provider for an evaluation. 

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Genetics

Genetic variations can influence FAI levels. Polymorphisms in genes that regulate the production of SHBG, testosterone, or enzymes involved in androgen biosynthesis and metabolism might affect the FAI value.

A condition called androgen insensitivity syndrome (AIS), caused by mutations in the androgen receptor gene, leads to decreased responsiveness of target tissues to testosterone, thereby affecting FAI levels.^[5]

Genome-wide association studies have identified several genetic variants associated with altered SHBG levels, which would consequently impact FAI calculations.^[6,7]

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Recommendations

• Regular monitoring of FAI levels can help to understand the hormonal health status over time, especially in people with conditions related to androgen levels.
• Adopting a balanced diet and regular exercise routine can help to maintain healthy FAI levels. Obesity has been linked to hormonal imbalances, so maintaining a healthy weight may be beneficial.
• If FAI values are outside the normal range, it's recommended to consult a healthcare provider for a thorough examination and diagnosis. 
• Certain medications can affect FAI levels. Consider discussing with your healthcare provider if you're taking any prescription drugs.

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The information and tests provided on our website are for educational purposes only and are not a substitute for professional medical advice. Always consult with your healthcare provider before making health decisions. Our tests do not diagnose or treat diseases. Individual results may vary and should be discussed with a healthcare provider.