When I check thyroid function and am suspicious, I look at TSH, fT3, fT4, thyroid antibodies, and sometimes revT3. The numbers must be carefully assessed in conjunction with symptoms. The standard normative scales don't work for many individuals. The good news is that not everyone needs thyroid replacement - as Dr. Romm outlines.
"Make sure your diet and your daily supplement provide you with iodine, selenium, and zinc which are three key nutrients needed by the thyroid gland for basic functioning. Sea vegetables such as 1 tablespoon of dulse flakes daily provides you with a nice dose of iodine, just 1-2 Brazil nuts each day provide you with ample selenium, and zinc is found in beef, oysters, dark meat chicken, cashews, pumpkin seeds, almonds, yogurt, and many other sources."