- T3 radioimmunoassay
A T3 test is done to evaluate the function of the thyroid gland. The healthcare professional may order the test if an individual shows signs of an overactive or underactive thyroid.
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 After the needle is withdrawn, the puncture site is covered for a short time to prevent bleeding.
What is involved in preparation for the test?
Generally no preparation is needed for a T3 test.
What do the test results mean?
The amount of T3 in blood normally ranges from 100 to 200 nanograms per deciliter (ng/dL). Abnormally high levels of T3 may indicate the following:
hyperthyroidism, that is, an overactive thyroid
- T3 thyrotoxicosis, a condition in which the body tissues are exposed to excessive amounts of T3
- thyroiditis, which is an inflammation of the thyroid
Abnormally low levels of T3 may indicate the following:
- chronic illness
Hashimoto's disease, an autoimmune disorderin which the body attacks its own thyroid gland for no known reason hypothyroidism, that is, an underactive thyroid