T3

Alternate Names : Triiodothyronine, T3 Radioimmunoassay

A T3 test measures the amount of the thyroid hormone T3 in the person's blood. Thyroid hormone, which is also called thyroxine or T4, is converted to T3 within cells. A T3 test is part of a series of thyroid function tests.

Who is a candidate for the test?

A T3 test is done to evaluate the function of the thyroid gland. The healthcare provider may order the test if an individual shows signs of an overactive or underactive thyroid.

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 After the needle is withdrawn, the puncture site is covered for a short time to prevent bleeding.