Cause of constant low t4 free, but normal t4, t3 (liothyronine) and tsh?

Level of TBG: All laboratory results need to be interpreted in the clinical context and the doctor who ordered the tests is usually in the best position to do that. Having said that, if you have high level of thyroglobulin binding protein (TBG) that will make your total T4 high when free T4 may be low. However, if your TSH is in the normal range, you are not likely to be thyroid deficient.