High SHBG: what it means

Sex hormone binding globulin is made in the liver. Lab Tests Online UK explains that it binds tightly to testosterone, dihydrotestosterone (DHT) and oestradiol and transports them in the blood in an inactive form. Normally, about 45% of testosterone in men and about 70% in women is tightly bound to SHBG, most of the rest is loosely bound to albumin, and only about 1 to 3% is free and immediately available to the tissues.

A total testosterone test measures all of this together and does not distinguish bound from free hormone. In many people that is enough. If SHBG is not normal, though, the total testosterone figure may be misleading, which is the main reason SHBG is measured.

When SHBG is increased beyond what is expected, Lab Tests Online UK says there is likely to be less free testosterone available than the total figure suggests. In men this could contribute to poor libido, even when total testosterone looks normal or borderline.

Laboratories often estimate free testosterone from total testosterone and SHBG, using a formula or the Free Androgen Index (total testosterone divided by SHBG). Generally such calculations are not recommended as first-line tests as they do not, in most cases, give more information than testosterone alone. In a person with a high SHBG, however, the calculated free fraction is exactly what clinicians want to see, so the combination of numbers matters more than one value.

Because SHBG is produced by the liver and controlled by several hormones, many things can push it up. The sources used for this page agree on a group of main causes.

• Liver disease. Hepatic dysfunction was the most common finding (12 of 45 men) in a retrospective study of raised SHBG from a Welsh teaching hospital.

• An overactive thyroid (hyperthyroidism or thyrotoxicosis), listed by Lab Tests Online UK and the same hospital study.

• Oestrogen exposure, including hormone replacement therapy and oral contraceptives, and rarely oestrogen-secreting tumours.

• Anorexia and nutritional problems, including deficiencies after gastrointestinal surgery.

• Medicines, including enzyme-inducing anticonvulsants such as carbamazepine and phenytoin.

• Growth hormone deficiency, and normal ageing in men.

• Anabolic steroid use. The Welsh study saw raised SHBG in five men that normalised after stopping, although Lab Tests Online UK says androgen use usually lowers SHBG, so the picture is not uniform.

In the Welsh hospital study, 45 men were included after exclusions, of whom 12 had hepatic dysfunction, 8 were taking relevant medicines, 5 had hyperthyroidism, 5 had used anabolic steroids and 3 had type 1 diabetes with no other cause. Three were explained by increased age, and 5 had no known cause. This was a small single-centre study presented as a conference abstract, so it illustrates the range of causes rather than their exact frequency.

In women, Lab Tests Online UK says SHBG with total testosterone is used to investigate testosterone production, and that decreased SHBG leaves more testosterone available, which could lead to hirsutism. A raised SHBG in a woman has the opposite effect on free testosterone, and oestrogen-containing contraception and hormone replacement are among the recognised causes.

Follow-up looks for the cause rather than treating the number. A clinician will normally review medicines (including hormones, anticonvulsants and any supplements or steroids), alcohol intake, weight loss, and symptoms of thyroid overactivity or liver disease. Liver blood tests and thyroid function tests (TSH and free T4) are the natural first steps.

Lab Tests Online UK adds that you cannot change SHBG directly and there is no reason to try, because SHBG is present to maintain the right level of testosterone entering the tissues. Treating the underlying cause is what normalises it. For example, the Welsh study reported that levels normalised after anabolic steroids were stopped.

If testosterone treatment is being considered, the free testosterone is the figure that guides decisions, so ask the clinician how the SHBG result has been taken into account.

A high SHBG on its own is not an emergency. Book a routine GP appointment if you have persistent low libido, erectile problems, fatigue or changes in periods along with the result. Seek prompt medical advice if you have yellowing of the skin or eyes, severe weight loss, palpitations with heat intolerance or sweating, or new breast changes, because these may point to the liver, thyroid or hormone problems behind the number.