Click here to return to the LMHS Home Page

 

Print-Friendly
Bookmarks

TBG - blood test

Serum thyroxine binding globulin; TBG level; Serum TBG level

 

The TBG blood test measures the level of a protein that moves thyroid hormone throughout your body. The protein is called thyroxine binding globulin (TBG).

How the Test is Performed

 

A blood sample is needed. The sample is sent to a laboratory. There it is examined using special tests such as electrophoresis or radioimmunoassay.

 

How to Prepare for the Test

 

Certain drugs and medicines can affect test results. Your doctor may tell you to temporarily stop taking a certain medicine before the test. Never stop taking any medicine without first talking to your doctor.

The following drugs can increase TBG level:

  • Estrogens, found in birth control pills and estrogen replacement therapy
  • Heroin
  • Methadone
  • Phenothiazines

The following medicines can decrease TBG levels:

  • Depakote or depakene (also called valproic acid)
  • Dilantin (also called phenytoin)
  • High doses of salicylates, including aspirin
  • Male hormones, including androgens and testosterone
  • Prednisone

 

How the Test will Feel

 

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.

 

Why the Test is Performed

 

This test may be done to diagnose problems with your thyroid, including thyroid disorders such as hypothyroidism.

 

Normal Results

 

If electrophoresis is used, normal values may range from 10 milligrams per 100 milliliters (mg/100 mL) to 24 mg/100 mL.

If radioimmunoassay is used, a normal range is 1.3 to 2.0 mg/100 mL.

Normal value ranges may vary slightly among different laboratories. Some labs use different measurements or may test different samples. Talk to your doctor about the meaning of your specific test results.

 

What Abnormal Results Mean

 

An increased TBG level may be due to:

  • Acute intermittent porphyria
  • Hypothyroidism
  • Liver disease
  • Pregnancy (TBG levels are normally increased during pregnancy)

Note: TBG levels are normally high in newborns.

Decreased TBG levels may be due to:

  • Acute illness
  • Acromegaly
  • Hyperthyroidism
  • Malnutrition
  • Nephrotic syndrome
  • Stress from surgery

 

Risks

 

Veins and arteries vary in size from one patient 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 associated with having blood drawn are slight but may include:

  • Excessive bleeding
  • Fainting or feeling light-headed
  • Hematoma (blood accumulating under the skin)
  • Infection (a slight risk any time the skin is broken)

 

 

References

Salvatore D, Davies TF, Schlumberger MJ, et al. Thyroid physiology and diagnostic evaluation of patients with thyroid disorders. In: Melmed S, Polonsky KS, Larsen PR, Kronenberg HM, eds. Williams Textbook of Endocrinology. 12th ed. Philadelphia, PA: Elsevier Saunders; 2011:chap 11.

BACK TO TOPText only

 
  • Blood test

    Blood test

    illustration

    • Blood test

      Blood test

      illustration

    A Closer Look

     

      Talking to your MD

       

        Self Care

         

          Tests for TBG - blood test

           
           

          Review Date: 5/10/2014

          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, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.

          The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition. A licensed medical professional should be consulted for diagnosis and treatment of any and all medical conditions. Links to other sites are provided for information only -- they do not constitute endorsements of those other sites. © 1997- A.D.A.M., Inc. Any duplication or distribution of the information contained herein is strictly prohibited.
          adam.com

           
           
           

           

           

          A.D.A.M. content is best viewed in IE9 or above, Firefox and Google Chrome browser.