A Sex Hormone Binding Globulin (SHBG) test is most commonly used to evaluate the status of a patient's androgens – the male hormones. With men, the issue of concern is testosterone deficiency, while with women the concern is excess testosterone production.
The SHBG test measures the concentration of SHBG in the blood. SHBG is a protein produced by the liver. SHBG binds tightly to testosterone, dihydrotestosterone (DHT), and estradiol (an estrogen) before transporting them in the blood in a metabolically inactive form.
The amount of SHBG in circulation is affected by age and sex. Concentrations are normally high in children; after puberty, SHBG levels decrease more rapidly in males than in females. Levels normally remain stable in adults and begin to increase in the elderly male at the same time that total testosterone levels begin to decrease. In postmenopausal women, SHBG, testosterone, and estrogen concentrations all decrease as hormone production by the ovaries tapers off.
A total testosterone test does not distinguish between bound and unbound testosterone; it only determines the overall quantity of testosterone. This is usually suitable for determining whether there is excessive or deficient testosterone production, but if SHBG levels are not normal, then the total testosterone value may be an inaccurate measure of the amount of testosterone that is available to a patient's tissues. Therefore, the most common reason to have this test performed is to discover whether the concentration of SHBG is affecting the amount of testosterone available to the body's tissues.
For men: SHBG and testosterone levels may be ordered to help determine the cause of infertility, a decreased sex drive, or erectile dysfunction, especially when total testosterone test results are inconsistent with clinical signs.
For women: Small amounts of testosterone are produced by the ovaries and adrenal glands. Even slight increases in testosterone production, caused for example by polycystic ovarian syndrome, can cause hormone imbalance and lead to conditions such as amenorrhea, infertility, acne, and hirsutism.
Bioavailability of the sex hormones testosterone and estradiol is influenced by the level of SHBG, which decreases the active form of the hormones that is available to the body. High levels of insulin and androgens decrease SHBG level, whereas thyroid hormone and estrogen increase it. It is also affected by decreased or increased testosterone or estrogen production.
Conditions with low SHBG include ovarian cysts, diabetes, hypothyroidism, obesity, Cushing's disease, and androgen use. Conditions with high SHBG include pregnancy, hyperthyroidism, liver disease, anorexia, and estrogen use. There has recently been research to link high SHBG levels with breast and testicular cancer as well.
Fasting is not required for this test. Take all medications as prescribed, but do not take supplements on the day of the test. The blood sample to be tested is drawn from a vein in your arm.
Related tests for determining hormone balance include Testosterone, Free Testosterone, Bioavailable Testosterone, Albumin level, Prolactin, Estradiol, Luteinizing Hormone.