Free Androgen Index

July 21, 2020

What is Androgen?

Androgen is a term which defines hormones which produce male characteristics such as facial hair. They are also present in females in small amounts. The free androgen index gives an estimate of how much free testosterone is present in the blood.[1]

What role does Free Androgen Index (FAI) play in the body?

Testosterone is present in larger amounts in men and stimulates body hair growth, the enlargement of the penis, the development of muscles and the deepening of the voice. The production of testosterone is controlled by another hormone, luteinising hormone (LH), which is made in the pituitary gland in the brain.

Women have a small amount of testosterone in their body. Testosterone is made in the adrenal glands in males and females. The adrenal glands are located just above the kidneys.

The testosterone circulating in the body is bound to albumin and sex hormone-binding globulin (SHBG). Free testosterone accounts for around 2% of the total testosterone and is the form that is biologically active.[2] Therefore, FAI is calculated using the total testosterone test result and SHBG result to help indicate the amount of active testosterone present.

How does FAI affect my wellbeing?


Low testosterone levels in men can lead to a reduction in sex drive. Testosterone deficiency is common in men who also have type 2 diabetes, causing low mood, reduced performance and low libido.[3]

High levels of testosterone are usually found in boys and causes the onset of early puberty. Testicular tumours are also a cause of increased testosterone levels.[4]


Moderately high testosterone in women can be caused by Polycystic Ovary Syndrome (PCOS).[5] PCOS can cause male features to develop such as facial hair as well as weight gain and irregular periods. The development of male features and weight gain can have a profound effect on mental health and self-esteem.[6]

How can I improve my result?

Weight loss and exercise can be beneficial, particularly for those who have low testosterone and type 2 diabetes.[3]

Some studies have shown that controlling diet can be useful for preventing weight gain but not necessarily for the biochemical symptoms of PCOS.[7]

Diet is also an important factor in the development of low testosterone. Increased fatty tissue and insulin resistance, both of which are linked to obesity, can be linked with testosterone deficiency.[8]

Ensure you are getting a good range of food types in your diet. If you haven’t already, you should increase the amount of fruit, vegetables and wholegrains you consume. For a healthy liver, you should keep your alcohol intake within the recommended guidelines of 14 units per week.

There is evidence that there are significant benefits of regular exercise on overall fitness, the cardiovascular system, health-related quality of life and nutritional parameters.[9]

However, exercise has major benefits for our wellbeing too. Exercise can help to reduce the symptoms of depression, self-esteem and anxiety.

We should all aim for around 150 minutes of aerobic exercise per week. Activities may include jogging, walking, swimming, cycling, exercise classes, sports matches or tennis.

- Health scores calculated



[1] GP Notebook. (2018). Free Androgen Index Test (FAI). Available at:

[2] Ho, C, K, M., Stoddart, M., Walton, M., Anderson, R, A and Beckett, G, J. (2006). Calculated Free Testosterone in Men: Comparison of Four Equations and With Free Androgen Index. The Association for Clinical Biochemistry: 43, pp 389-397.

[3] Grossmann, M., Thomas, M, C., Panagiotopoulos, S., Sharpe, K., MacIsaac, R, J., Clarke, S, Zajac, J, D and Jerums, G. (2008). Low Testosterone Levels are Common and Associated with Insulin Resistance in Men with Diabetes. The Journal of Clinical Endocrinology and Metabolism: 93(5), pp 1834-1840.

[4] Porcaro, A, B., Petrozziello, A and Brunelli, M et al., (2016). Prostate Cancer Volume Associates with Preoperative Plasma Levels of Testosterone that Independently Predicts High Grade Tumours Which Show Low Densities (Quotient Testosterone/Tumour Volume). Asian Journal of Urology: 3(1), pp 26-32.

[5] Pasquali, R., Zanotti, L and Fanelli, F et al., (2016). Defining Hyperandrogenism in Women with Polycystic Ovary Syndrome: A Challenging Perspective. J Clin Endocrinol Metab: 101(5), pp 2013-2022.

[6] McCartney, C, R and Marshall, J, C. (2016). Polycystic Ovary Syndrome. The New England Journal of Medicine: 375(1), pp 54-64.

[7] Wong, J, M, W., Gallagher, M and Gooding, H et al., (2016). A Randomized Pilot Study of Dietary Treatments for Polycystic Ovary Syndrome in Adolescents. Pediatr Obes: 11(3), pp 210-220.

[8] Body, A., White, D and Garcia, J, M. (2015). Relevance of Low Testosterone to Non-Alcoholic Fatty Liver Disease. Cardiovasc Endocrinol: 4(3), pp 83-89.

[9] Heiwe, S and Jacobson, S, H (2011). Exercise Training for Adults with Chronic Kidney Disease (Review). Cochrane Database of Systematic Reviews: 10.

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This information has been medically reviewed by Dr Nicky Keay

Nicola has extensive clinical and research experience in the fields of endocrinology and sport and exercise medicine. Nicky is a member of the Royal College of Physicians, Honorary Fellow in the Department of Sport and Exercise Sciences at Durham University and former Research Fellow at St. Thomas' Hospital.

Dr Nicky Keay

Dr Nicky Keay

BA, MA (Cantab), MB, BChir, MRCP.