The TBG blood test measures the level of a protein that moves thyroid hormone throughout your body. This protein is called thyroxine binding globulin (TBG).
A blood sample is taken and then sent to a laboratory for testing.
Certain drugs and medicines can affect test results. Your health care provider may tell you to stop taking a certain medicine for a short time before the test. Never stop taking any medicine without first talking to your provider.
These medicines and drugs can increase TBG level:
The following medicines can decrease TBG levels:
When the needle is inserted to draw blood, some people feel moderate pain. Others feel only a prick or stinging. Afterward, there may be some throbbing or slight bruising. This soon goes away.
This test may be done to diagnose problems with your thyroid.
Normal range is 13 to 39 micrograms per deciliter (µg/dL), or 150 to 360 nanomoles per liter (nmol/L).
Normal value ranges may vary slightly among different laboratories. Some labs use different measurements or may test different samples. Talk to your provider about the meaning of your specific test results.
An increased TBG level may be due to:
Note: TBG levels are normally high in newborns.
Decreased TBG levels may be due to:
There is little risk involved with having your blood taken. Veins and arteries vary in size from one person to another and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others.
Other risks of having blood drawn are slight, but may include:
Reviewed By: Brent Wisse, MD, Associate Professor of Medicine, Division of Metabolism, Endocrinology & Nutrition, University of Washington School of Medicine, Seattle, WA. Also reviewed by David Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.