TT3 is the main hormone that thyroid hormone does to various target organs. The serum TT3 concentration reflects the thyroid gland’s ability to function better than the thyroid gland. TT3 is an important indicator of early hyperthyroidism and the monitoring of recurrent hyperthyroidism and pseudo thyrotoxicosis.

Clinical Significance
If your results show high total T3 levels or high free T3 levels, it may mean you have hyperthyroidism. Low T3 levels may mean you have hypothyroidism, a condition in which your body doesn't make enough thyroid hormone.
T3 test results are often compared with T4 and TSH test results to help diagnose thyroid disease.

Intent Use

A T3 test is most often used to diagnose hyperthyroidism, a condition in which the body makes too much thyroid hormone.T3 tests are frequently ordered with T4 and TSH (thyroid stimulating hormone) tests. A T3 test may also be used to monitor treatment for thyroid disease.