Locations Main Campus: Chesterfield, MO 63017   |   Locations
314-434-1500 314-434-1500   |   Contact Us

Multimedia Encyclopedia

BACK
TO
TOP
 
E-mail Form
Email Results

 
 
Print-Friendly
Bookmarks
bookmarks-menu

Free T4 test

Thyroxine test; Total T4 test

 

T4 (thyroxine) is the main hormone produced by the thyroid gland. A laboratory test can be done to measure the amount of free T4 in your blood.

How the Test is Performed

 

A blood sample is needed.

 

How to Prepare for the Test

 

Your health care provider will tell you if you need to stop taking any medicines that may affect the test result. In general, test results are not affected by other medicines you may be taking.

Pregnancy and some diseases, including kidney and liver disease, can affect the results of this test.

 

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 a slight bruise. This soon goes away.

 

Why the Test is Performed

 

Your provider may recommend this test if you have signs of a thyroid disorder, including:

  • Abnormal findings of other thyroid blood tests, such as TSH or T3
  • Symptoms of an overactive thyroid
  • Symptoms of an underactive thyroid
  • Hypopituitarism (the pituitary gland does not produce enough of its hormones)
  • Lump or nodule in the thyroid
  • Enlarged or irregular thyroid gland
  • Problems becoming pregnant

This test is also used to monitor people who are being treated for thyroid problems.

 

Normal Results

 

A typical normal range is 4.5 to 11.2 micrograms per deciliter (mcg/dL) or 57919.50 to 144155.20 picomoles per liter (picomol/L).

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

 

What Abnormal Results Mean

 

To fully understand results of the free T4 test, results of other thyroid blood tests, such as TSH or T3, may be needed.

Test results may also be affected by pregnancy, estrogen level, liver problems, more severe body-wide illnesses, and inherited changes in a protein that binds T4.

A higher than normal level of T4 may be due to conditions that involve an overactive thyroid, including:

  • Graves disease
  • Taking too much thyroid hormone medicine
  • Thyroiditis
  • Toxic goiter or toxic thyroid nodules
  • Some tumors of the testes or ovaries (rare)
  • Getting medical imaging tests with contrast dye that contains iodine (rare, and only if there is a problem with the thyroid)
  • Eating a lot of foods that contain iodine (very rare, and only if there is a problem with the thyroid)

A lower than normal level of T4 may be due to:

  • Hypothyroidism (including Hashimoto disease and other disorders involving an underactive thyroid)
  • Severe acute illness
  • Malnutrition or fasting
  • Use of certain medicines

 

Risks

 

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 associated with having blood drawn are slight but may include:

  • Excessive bleeding
  • Fainting or feeling lightheaded
  • Hematoma (blood buildup under the skin)
  • Infection (a slight risk any time the skin is broken)

 

 

Open References

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, Larsen PR, et al, eds. Williams Textbook of Endocrinology . 12th ed. Philadelphia, PA: Elsevier Saunders; 2011:chap 11.

Weiss RE, Refetoff S. Thyroid function testing. In: Jameson JL, De Groot LJ, eds. Endocrinology: Adult and Pediatric . 7th ed. Philadelphia, PA: Elsevier Saunders; 2016:chap 78.

 
  • Blood test

    Blood test - illustration

    Blood is drawn from a vein (venipuncture), usually from the inside of the elbow or the back of the hand. A needle is inserted into the vein, and the blood is collected in an air-tight vial or a syringe. Preparation may vary depending on the specific test.

    Blood test

    illustration

    • Blood test

      Blood test - illustration

      Blood is drawn from a vein (venipuncture), usually from the inside of the elbow or the back of the hand. A needle is inserted into the vein, and the blood is collected in an air-tight vial or a syringe. Preparation may vary depending on the specific test.

      Blood test

      illustration

    A Closer Look

     

      Self Care

       

        Tests for Free T4 test

         
         

        Review Date: 2/3/2016

        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.

         
         
         

         

         

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



        Content is best viewed in IE9 or above, Firefox and Google Chrome browser.