Print this article
Share this page:
Also known as: Testosterone-oestrogen binding globulin; ToBG
Formal name: Sex hormone binding globulin
Related tests: Testosterone; free testosterone; bioavailable testosterone

At a Glance

Why Get Tested?

To help evaluate whether the concentration of SHBG is affecting the amount of testosterone available to the body’s tissues

When to Get Tested?

If your total testosterone results seem inconsistent with clinical signs, suggesting a testosterone deficiency or excess production

Sample Required?

A blood sample drawn from a vein in your arm

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. It binds tightly to testosterone, dihydrotestosterone (DHT), and oestradiol (an oestrogen) 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 oestrogen 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.

A total testosterone does not distinguish between bound and unbound testosterone; it determines the overall quantity of testosterone. In many cases, this is sufficient to evaluate excessive or deficient testosterone production; but, if a patient’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 a patient’s tissues.

How is the sample collected for testing?

A blood sample is obtained by inserting a needle into a vein in the arm.

The Test

Common Questions

Ask a Laboratory Scientist

Article Sources

« Return to Related Pages

NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used.