Sex hormone binding globulin (SHBG) is a protein made in the liver responsible for transporting inactive forms of the hormones, oestradiol, testosterone and dihydrotestosterone.
An SHBG test measures how much of the protein is in the blood. The concentration of SHBG in the blood depends upon both age and gender as well as by increased or decreased levels of the hormones it transports. 
An SHBG test is usually used to find out how much testosterone is being delivered to the tissues in the body. It’s often used in men who are experiencing the symptoms of low testosterone and in women it’s used if they have symptoms of high testosterone levels.
You can test your SHBG levels alongside key fertility hormones by purchasing a simple at-home finger prick test kit which is then analysed at an accredited lab. Forth offers a number of blood tests which include SHBG such Female Fertility, Male Hormones, Menopause Health and our Vitality package which includes analysis of over 30 key biomarkers for good health.
In the human body, SHBG is a high-affinity binding protein for the androgen, testosterone and the oestrogen, oestradiol. Only small amounts of these hormones are ‘free’ in circulation. Once these hormones attach to SHBG they are inactive, therefore the availability of these sex hormones is influenced by the amount of SHBG in the blood.
SHBG levels are normally higher in women than men and limit the exposure to testosterone and oestrogen.  Measuring SHBG levels can be used to indicate how much testosterone is available for use by the body. The amount of testosterone tightly bound to SHBG differs between men and women, approximately 45% in men and 70% in females. The rest is weakly bound to albumin or unbound and freely available. 
Increased levels of SHBG are often seen in elderly men or individuals who have an underactive thyroid or liver cirrhosis. Increased levels in women may be caused by the contraceptive pill, too. If levels of SHBG are increased, the amount of testosterone available to tissues is reduced.
Reduced levels of SHBG means there is a greater amount of free testosterone in circulation. In females, increased levels of free testosterone can cause polycystic ovary syndrome (PCOS). PCOS causes the loss of periods as well as some unpleasant symptoms.
If you are worried about your hormone levels or just want to check where you fall on the range, you can test your SHBG level with a simple at-home blood test.
Polycystic ovary syndrome affects the function of the ovaries and causes unwanted side effects.
The contraceptive pill or antiepileptic medication can also cause increased SHBG levels.
A decreased circulating testosterone and SHBG are risk factors for metabolic syndrome in elderly men. Metabolic syndrome is the name given to a combination of diabetes, high blood pressure and obesity. Metabolic syndrome increases the risk of coronary heart disease, stroke and cardiovascular disease.
If levels of SHBG are reduced in females, it can result in PCOS which causes the following symptoms:
PCOS affects 1 in 5 women of reproductive age. The condition also causes some psychological symptoms such as:
The symptoms of metabolic syndrome are:
Metabolic syndrome is diagnosed if you have at least 3 of these symptoms.
Diet and lifestyle choices can help to treat and control both PCOS and metabolic syndrome. Heart disease and diabetes are side effects of PCOS, as well as major factors in SHBG levels and so eating the right diet is key to preventing them. Eating a diet with low glycaemic index foods can be beneficial. Low GI foods raise blood sugar slowly which reduces the symptoms of PCOS and they help to manage diabetes.
Low glycaemic foods include:
Low GI foods are particularly useful in conditions which make individuals resistant to insulin. 
Being overweight is a risk factor for both metabolic disease and PCOS and increases the severity of these conditions. Physical activity is beneficial for weight loss but also improves the body’s response to insulin.
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 Selby, C. (1990). Sex Hormone Binding Globulin: Origin, Function and Clinical Significance. Ann Clin Biochem: 27, pp 532-541.
 Laurent, M, R et al. (2016). Sex Hormone-Binding Globulin Regulation of Androgen Bioactivity In Vivo: Validation of the Free Hormone Hypothesis. Scientific Reports.
 Bulun, S, E. (2015). Chapter 17 – Physiology and Pathology of the Female Reproductive Axis. In: Williams Textbook of Endocrinology, pp 589-663.
 Lab Tests Online UK. (2017). SHBG. Available at: https://labtestsonline.org.uk/tests/shbg
 Chubb, S, A, P et al. (2008). Lower Sex Hormone-Binding Globulin is More Strongly Associated with Metabolic Syndrome than Lower Total Testosterone in Older Men: The Health in Men Study. European Journal of Endocrinology: 158(6).
 Ehrmann, D, A. (2005). Polycystic Ovary Syndrome. The New England Journal of Medicine: 352, pp 1223-36.
 NHS. (2016). Metabolic Syndrome. Available at: https://www.nhs.uk/conditions/metabolic-syndrome/
 The Association of UK Dietitians. (2016). Polycystic Ovary Syndrome (PCOS). Available at: https://www.bda.uk.com/foodfacts/pcos.pdf