TSH then stimulates cells in your thyroid to release thyroxine or T4 (80%) and triiodothyronine or T3 (20%) into your bloodstream. These two hormones prevent your pituitary gland from producing more TSH if the levels of thyroxine and triiodothyronine are too high, thus completing the cycle. When T4 and T3 levels drop, the cycle starts over again.

If my T3 and T4 and reverse T3 are sin the normal range my TSH is always low. Usually less than 0.1. If my TSH is even close to 0.3 my T3 and T4 are below the normal range. In case of the T3 quite a bit below normal. I took synthroid for about 18 years and everything was okay. A couple of years ago my T3’s dropped like a rock.

High levels of TSH is an indicator that your thyroid is not producing enough hormones, like thyroxine (T4) and or triiodothyronine (T3). This hormonal imbalance is called primary hypothyroidism. Sometimes high TSH causes a decrease in thyroid hormones, but they are still in normal range. This is called subclinical hypothyroidism.