What is sex-hormone binding globulin (SHBG)?
Sex hormone binding globulin (SHBG) is a protein produced by the liver that binds tightly to the hormones testosterone, dihydrotestosterone (DHT), and Estradiol (a type of estrogen). SHBG transports these hormones in the blood as biologically inactive forms. This test measures the level of SHBG in the blood and is most often used to help evaluate testosterone deficiency or excess.
When your SHBG levels are high, your body has fewer free sex hormones at its disposal, decreasing their effects. When SHBG is low your body has more free sex hormones at its disposal. SHBG transports these hormones in the blood as biologically inactive forms.
Why test sex-hormone binding globulin (SHBG)?
Unless this is ordered as a retest or for a specific reason, we recommend ordering this as part of a health test.
Symptoms
If you have signs and/or symptoms of having too much or too little testosterone. This test is valuable for suspected low testosterone in men, as well as for women with signs of excess androgens.
What causes low SHBG?
A low SHGB indicates that more total testosterone is unbound (bioactive) and available to the tissues than the total testosterone level test suggests. Men typically have lower SHBG levels than women. It is important to consider the results of this test in the context of other tests and the clinical picture. SHBG can be important in determining whether someone has a hormone problem. The following may lower SHBG: high insulin levels, obesity, high prolactin levels, inflammation, hypothyroidism, Cushing Disease (abnormally high levels of cortisol), nonalcoholic fatty liver disease, acromegaly, (too much growth hormone in adults), androgen steroid use, and genetic factors.
In men, low SHBG often means high free testosterone, which can lead to symptoms like fluid retention, acne, increased appetite, weight gain, muscle mass, and mood swings. Excess estrogen in men can cause erectile dysfunction and larger breast tissue.
In women, low SHBG can lead to too much available testosterone, and this can result in weight gain, excess facial and body hair, acne, mood swings, and menstrual changes. Too much available estrogen can lead to irregular periods, mood swings, bloating, and breast tenderness.
Women with PCOS may have low SHBG levels and tend to have insulin resistance, be overweight, and have excess androgen production.
What causes high SHBG?
A high SHGB indicates that less total testosterone is unbound bioactive and available to the tissues than the total testosterone level test suggests. High SHGB levels decrease the effects of sex hormones available in the body (especially testosterone) by binding to them. SHBG reduces the availability of testosterone, so some people may wish to lower their SHBG levels. SHBG can be important in determining whether someone has a hormone problem. A man’s SHBG level usually increases with age as his testosterone levels drop.
SHBG can be important in determining whether someone has a hormone problem. Liver conditions, hyperthyroidism and raised T3 and/or T4, eating disorders, HRT, decreased sex hormone production, pregnancy, growth hormone deficiency, alcohol consumption, smoking, and Alzheimer’s disease can all increase SHBG levels.
More information
In men, about 45% to 65% of testosterone in the blood is normally bound to SHBG, with the remainder weakly and reversibly bound to albumin (the main protein in the blood). Only about 2% to 3% of testosterone is immediately available to the tissues as free testosterone. Testosterone that is weakly bound to albumin is also bioavailable and can be readily taken up by the body's tissues.
In women, slightly more testosterone (66% to 78%) is bound to SHBG. In women, SHBG plays an integral role in regulating the levels of bioavailable male sex hormones (androgens) and estrogens circulating throughout the body. As SHBG has a higher affinity for the androgens testosterone and DHT, women with low SHBG may have signs and symptoms related to androgen excess.
A total testosterone test does not distinguish between bound and unbound testosterone but determines the overall quantity of testosterone. In many cases, this is sufficient to evaluate excess or deficient testosterone production. However, if a person's SHBG level is not normal, then the total testosterone may be an inaccurate representation of the amount of testosterone that is available to the person's tissues. An SHBG test may be performed when a person's signs and symptoms do not correlate with the results of a total testosterone test.
Instructions
No advance preparation is needed for this test.
On the day of the test
Remember to take I.D. with you when going to take a test. Do not work out before going to do this test, as this may affect your results. Arrive early and sit down quietly before taking this test.