Free Triiodothyronine (FT3)

What is T3 test (triiodothyronine)?

T3 test (triiodothyronine) is a test that measures the blood level of the hormone. Some of which is produced directly by the thyroid gland (kidshealth). It is also used to monitor thyroid replacement and suppressive therapy.

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Why do you need to take this test?

Doctors may order the T3 test when a child’s symptoms or previous blood tests suggest thyroid dysfunction. The T3 test is particularly useful in diagnosing hyperthyroidism, a condition in which the thyroid overproduces hormones, causing symptoms such as a fast heart rate, weight loss, trembling and sweating (kidshealth).


There is no special preparation for this test. However, you should tell the doctor about the medicines that you take. It is because it might affect the results of the tests.


Typically, normal results range from 100 to 200 nanograms per deciliter (ng/dL). Higher than that range means abnormal.

A normal T3 test result doesn’t necessarily mean that your thyroid is functioning perfectly. Measuring your T4 and TSH can help your doctor figure out if you have a thyroid problem despite a normal T3 result.

Any questions? Please don’t hesitate to contact us. We will do our best to help you.