Most Doctors order a TSH test and feel that it is adequate. Unfortunately that test is inversely related to the amount of thyroid produced, so we measure the Free-T4 and Free-T3 levels. There is an entire featured article on Thyroid which I suggest you look at on this site that explains our philosophy of treating patients with thyroid disorders. Click Here to go to that article. In essence, there are two thyroid Hormones T4 and T3. T3 is the active one and most doctors prescribe Synthroid (T4). Some people cannot convert T4 to T3 and they can be identified by our type of thyroid testing.