Hormones
SHBG
The protein that binds testosterone and estradiol in the blood; needed to know how much testosterone is actually active.
Everything about this testWhat it measures
SHBG (sex hormone-binding globulin) is made in the liver and binds testosterone and estradiol, which makes them inactive. In men about half of the testosterone is bound to SHBG, in women about three quarters. The higher the SHBG, the less free testosterone remains at the same total value. The result is therefore almost always used together with total testosterone to calculate free testosterone.
- An abnormal amount of active testosterone in men in whom the total value is hard to interpret (overweight, older age, liver disease)
- Too much active male hormone in women with PCOS, excess hair growth or an irregular cycle: SHBG is often low in these cases
- A sign of insulin resistance or a thyroid disorder, which strongly affect SHBG
High
A raised SHBG means that less free testosterone is available than the total testosterone suggests. Common causes are the contraceptive pill and other estrogens, pregnancy, an overactive thyroid, liver disease, older age and underweight. In men with a raised SHBG, total testosterone can be normal while there is still a shortage of active hormone.
Low
A low SHBG means that more free testosterone is available than the total value shows. It is common with overweight, insulin resistance and type 2 diabetes, with an underactive thyroid, with use of anabolic steroids or testosterone, and in women with PCOS. In men with overweight, this is the reason that a low total testosterone often still comes with a normal free testosterone.
Preparation
- Do you take biotin (vitamin B8, often in hair and nail supplements)? Stop at least 2 days before the sample is taken, or 4 days for a high dose.
If your result is abnormal
The GP uses SHBG to calculate free testosterone and assesses this together with the symptoms and total testosterone. With a markedly abnormal SHBG without a clear cause, thyroid or liver function is sometimes checked.
Reliability
SHBG is not a disease marker on its own but a supporting value: it tells you how total testosterone should be read. The guidance of the Dutch Society for Endocrinology (NVE) advises measuring SHBG as well if total testosterone is in the borderline range or if there is a reason for an abnormal SHBG, such as overweight or liver disease. The measurement itself is stable and has little daily rhythm; interpretation always needs total testosterone as well.
Limitations
- Estrogens (the pill, hormone therapy), pregnancy and a thyroid disorder strongly raise or lower SHBG without anything being wrong with the sex hormones.
- Overweight, insulin resistance, anabolic steroids and corticosteroids lower SHBG.
- A stand-alone SHBG without total testosterone cannot be interpreted; the calculation of free testosterone differs between laboratories.
How common is this
SHBG abnormalities are not a disease in themselves. They occur mainly in common situations: overweight and type 2 diabetes (low SHBG), pill use and older age (high SHBG). Among women of childbearing age, about 5 to 10 in 100 have PCOS, in which SHBG is often low.
Who is this useful for
Useful together with total testosterone: in men with symptoms of testosterone deficiency, especially with overweight, liver disease or older age, and in women with excess hair growth, acne or an irregular cycle in whom PCOS is being considered. As a stand-alone test without testosterone, SHBG has no value; in healthy people without symptoms, measuring it is not needed.
Downsides and risks
- An abnormal SHBG is sometimes seen as a problem in itself, while it is usually a result of pill use, weight or age and needs no treatment.
Sources
Always discuss an abnormal result with your GP. If a result is strongly abnormal, we try to reach you as soon as possible. Read your result yourself as well and contact your GP if in doubt. A test does not make a diagnosis. Read more about risks and results