Sex Hormone Binding Globulin (SHBG)

This is a test to help evaluate whether the concentration of SHBG is affecting the amount of testosterone available to the body's tissues. With men, the issue of concern is testosterone deficiency, while with women the concern is excess testosterone production.

The Sex Hormone Binding Globulin (SHBG) test measures the concentration of SHBG in the blood. SHBG is a protein that is produced by the liver. It binds tightly to testosterone, dihydrotestosterone (DHT), and estradiol (an estrogen) and transports them in the blood in a metabolically inactive form. The amount of SHBG in circulation is affected by age and sex, by decreased or increased testosterone or estrogen production, and can be affected by certain diseases and conditions such as liver disease, hyperthyroidism or hypothyroidism, and obesity.

Changes in SHBG concentrations can in turn affect the amount of testosterone that is available to be used by the body's tissues. Normally, about 40% to 60% of testosterone is bound to SHBG, and most of the rest is weakly and reversibly bound to albumin (another protein). Only about 2% is immediately available to the tissues as free testosterone.

PREPARATION FOR TEST

No preparation is needed. A blood sample drawn from a vein in your arm.

NORMAL FINDINGS

Your lab will provide a range of normal values with your test results.

Ranges for normal findings may vary among different laboratories and hospitals. You should always check with your doctor after having lab work or other tests done to discuss the meaning of your test results and whether your values are considered within normal limits.

MEANING OF TEST

Your caregiver will go over your test results with you and discuss the importance of this test. Reference values are dependent on many factors, including patient age, gender, sample population, and testing method. Numeric test results have different meanings in different labs. Your lab report should include the specific reference range for your test.

When SHBG levels are increased beyond what is expected, there is likely to be less free testosterone available to the tissues than is indicated by the total testosterone. If SHBG concentrations are decreased, more of the total testosterone is "bioavailable" (not bound to SHBG).

OBTAINING THE TEST RESULTS

It is your responsibility to obtain your test results. Ask the lab or department performing the test when and how you will get your results.