Banner image

T3 test

Triiodothyronine; T3 radioimmunoassay; Toxic nodular goiter - T3; Thyroiditis - T3; Thyrotoxicosis - T3; Graves disease - T3

Find

Learn More

Definition

Triiodothyronine (T3) is a thyroid hormone. It plays an important role in the body's control of metabolism (the many processes that control the rate of activity in cells and tissues).

A laboratory test can be done to measure the amount of T3 in your blood.

How the Test is Performed

A blood sample is needed.

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.

How to Prepare for the Test

Your health care provider will tell you if you need to stop taking any medicines before the test that may affect your test result. DO NOT stop taking any medicine without first talking to your provider.

Drugs that can increase T3 measurements include:

  • Birth control pills
  • Clofibrate
  • Estrogens
  • Methadone
  • Certain herbal remedies

Drugs that can decrease T3 measurements include:

  • Amiodarone
  • Anabolic steroids
  • Androgens
  • Antithyroid drugs (for example, propylthiouracil and methimazole)
  • Lithium
  • Phenytoin
  • Propranolol

Normal Results

The range for normal values are:

  • Total T3 -- 60 to 180 nanograms per deciliter (ng/dL), or 0.92 to 2.76 nanomoles per liter (nmol/L)
  • Free T3 -- 130 to 450 picgrams per deciliter (pg/dL), or 2.0 to 7.0 picomoles per liter (pmol/L)

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

Normal values are age specific for people less than age 20. Check with your provider about your specific results.

Risks

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 associated with having blood drawn are slight, but may include:

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

What Abnormal Results Mean

A higher-than-normal level of T3 may be a sign of:

A high level of T3 may occur in pregnancy (especially with morning sickness at the end of the first trimester) or with the use of birth control pills or estrogen.

A lower-than-normal level may be due to:

  • Severe short-term or some long-term illnesses
  • Thyroiditis (swelling or inflammation of the thyroid gland -- Hashimoto disease is the most common type)
  • Starvation
  • Underactive thyroid gland

Why the Test is Performed

This test is done to check your thyroid function. Thyroid function depends on the action of T3 and other hormones, including thyroid-stimulating hormone (TSH) and T4.

Sometimes it can be useful to measure both T3 and T4 when evaluating thyroid function.

The total T3 test measures the T3 that is both attached to proteins and floating free in the blood.

The free T3 test measures the T3 that is floating free in the blood. The tests for free T3 are generally less accurate than for total T3.

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

  • The pituitary gland does not produce normal amounts of some or all of its hormone (hypopituitarism)
  • Overactive thyroid gland (hyperthyroidism)
  • Underactive thyroid gland (hypothyroidism)
  • Taking medicines for hypothyroidism

Review Date: 2/22/2018
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.

ADAM QualityA.D.A.M., Inc. is accredited by URAC, also known as the American Accreditation HealthCare Commission (www.urac.org). URAC's accreditation program is an independent audit to verify that A.D.A.M. follows rigorous standards of quality and accountability. A.D.A.M. is among the first to achieve this important distinction for online health information and services. Learn more about A.D.A.M.'s editorial policy, editorial process and privacy policy. A.D.A.M. is also a founding member of Hi-Ethics and subscribes to the principles of the Health on the Net Foundation (www.hon.ch).

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. Call 9-1-1 for all medical emergencies. Links to other sites are provided for information only—they do not constitute endorsements of those other sites. © 1997-2010 A.D.A.M., Inc. Any duplication or distribution of the information contained herein is strictly prohibited.