The Test Sample
What is being tested?
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 and binds tightly to testosterone, dihydrotestosterone (DHT), and estradiol (an estrogen). In this bound state, it transports them in the blood as a biologically 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 levels can 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, with most of the rest weakly and reversibly bound to albumin, the main protein in the blood. Only about 2% is immediately available to the tissues as free testosterone.
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 excessive or deficient testosterone production. However, if a person's SHBG level is not normal, then the total testosterone may not be an accurate representation of the amount of testosterone that is available to the person's tissues.
How is the sample collected for testing?
A blood sample is obtained by inserting a needle into a vein in the arm.
NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.
Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.
Is any test preparation needed to ensure the quality of the sample?
No test preparation is needed.