Alternative Names triiodothyronine, T3 radioimmunoassay
Definition This test measures the amount of T3, which is a form of thyroid hormone, in the blood. The test is done to evaluate thyroid function, especially when a person is thought to have an overactive or underactive thyroid.
Thyroid hormone, which is also called thyroxin or T4, seems to be converted to T3 within cells. Thyroid hormone plays a large role in controlling the energy needed to keep the body functioning at rest.
How is the test performed? To measure the amount of T3 in the blood, a blood sample is taken from a vein on the forearm or hand. First, the skin over the vein is cleaned with an antiseptic. Next, a strong rubber tube, or tourniquet, is wrapped around the upper arm. This enlarges the veins in the lower arm by restricting blood flow through them. A fine needle is gently inserted into a vein, and the tourniquet is removed. Blood flows from the vein through the needle, and is collected into a syringe or vial for T3 testing in the laboratory. After the needle is withdrawn, the puncture site is covered for a short time to prevent bleeding.
What is involved in preparation for the test? A person should request specific instructions from his or her doctor.
What do the test results mean? The amount of free T3 in blood normally ranges from 2.5 to 5.5 pmols/L (picomoles pre litre).
Abnormally high levels of T3 may indicate the following:.
Author: David T. Moran, MD Reviewer: eknowhow Medical Review Panel Editor: Dr John Hearne Last Updated: 21/03/2005 Contributors Potential conflict of interest information for reviewers available on request
This website and article is not a substitute for independent professional advice. Nothing contained in this website is intended to be used as medical advice and it is not intended to be used to diagnose, treat, cure or prevent any disease, nor should it be used for therapeutic purposes or as a substitute for your own health professional's advice. All Health and any associated parties do not accept any liability for any injury, loss or damage incurred by use of or reliance on the information.