SHBG (sex hormone binding globulin) test

SHBG, or sex hormone binding globulin, is a protein produced mainly by the liver. In the blood it binds to the sex hormones — testosterone and oestrogen — and in that way controls how much of these hormones stays free, that is, biologically active and available to the tissues. A hormone bound to SHBG temporarily becomes inactive, so the amount of SHBG directly affects the body's overall hormonal balance, even if the total amount of testosterone or oestrogen in the blood is unchanged. That is why the SHBG test is most often done together with total testosterone, so that the amount of free (active) testosterone or the free androgen index can be calculated. The SHBG level is affected by the condition of the liver, thyroid function, body weight, insulin sensitivity and some medicines, so an altered result often reflects not the sex hormone system itself but a condition related to it.

• In men, when a testosterone deficiency is suspected — a reduced sex drive, erectile problems, tiredness, loss of muscle mass or fertility problems
• In women, when there are signs typical of a raised level of androgens — heavy hair growth on the face or body, a deepening voice, acne, irregular periods
• When polycystic ovary syndrome (PCOS) is suspected
• When assessing a total testosterone or oestrogen result, where the free (active) amount of the hormone has to be calculated
• In liver disease, a thyroid function disorder or with other signs that could affect SHBG production
• To monitor the effect of hormonal treatment or of contraception

The exact reference interval depends on the laboratory, on sex and on age, so you will find it on your own laboratory report. SHBG is most often assessed together with total testosterone or oestrogen, so that the amount of the free hormone can be calculated.

A raised SHBG

A raised SHBG reduces the amount of free (active) testosterone or oestrogen, even if the total amount of the hormone in the blood is normal. The most common causes are liver disease, hyperthyroidism, some eating disorders and oestrogen-containing medicines (for example, hormone therapy or contraceptive pills). In men, SHBG can also rise when the production of the sex hormones themselves falls.

• Liver disease
• Hyperthyroidism (an overactive thyroid)
• Some eating disorders
• Oestrogen-containing medicines — hormone therapy, contraceptive pills
• Reduced production of sex hormones in men

What is usually assessed alongside a raised SHBG:

• Liver function markers and thyroid tests (TSH, free T4)
• The medicines being taken, especially those containing oestrogen or other hormonal preparations
• Calculating the amount of free testosterone or oestrogen together with the total amount of the hormone
• Symptoms related to a deficiency of sex hormones in men

A low SHBG means that more of the sex hormones in the blood stay free and active. The most common causes are hypothyroidism, type 2 diabetes or insulin resistance, obesity, the use of steroid or anabolic medicines, Cushing's syndrome and, in women, polycystic ovary syndrome (PCOS). SHBG also decreases naturally with age.

• Hypothyroidism (an underactive thyroid)
• Type 2 diabetes or insulin resistance
• Obesity or being significantly overweight
• The use of steroid and anabolic medicines
• Cushing's syndrome
• Polycystic ovary syndrome (PCOS) in women
• The age-related decline in SHBG

Symptoms that may accompany a low level:

• In men: a reduced sex drive, erectile problems, tiredness, loss of muscle mass, fertility problems
• In women: heavy hair growth on the face or body, a deepening voice, irregular periods, acne, weight gain, fertility problems

What is usually assessed alongside a low SHBG:

• Thyroid function tests (TSH, free T4)
• Glucose and insulin resistance markers (glucose, HOMA-IR)
• Body weight and the conditions related to it
• Total and free testosterone or an androgen profile, especially in women when PCOS is suspected

Reading the result

The SHBG level is affected by the condition of the liver, thyroid function, body weight, insulin sensitivity and some medicines, so an altered result often reflects not the sex hormone system itself but a condition related to it. The exact reference interval depends on the laboratory, on sex and on age, so compare the number with the interval printed on your own report — the same logic that applies to reading blood test results generally.