Thyroid testing is rather a messy deal.
This is because most clinicians, if they are agile thinkers, realize that basic testing of TSH does not tell the practitioner enough if T3 signals, the most powerful thyroid signals, are getting to distant and vital tissues.
For years, basic testing has been TSH, the pituitary’s job in ruling thyroid.
Since then, functional doctors have repeatedly said, T4 has to be converted to T3.
This critical conversion can be hindered by stress (excess cortisol), inadequate minerals (selenium and zinc) and many other factors that keep piling up.
Most patients diagnosed with thyroid issues are given a script for T4. Often this T4 has many other additives in it like talc and gluten.
And who knows if the T4 converts to T3.
Thus, functional doctors have run more extensive panels including free T4, free T3, TSH, reverse T3 (that can block T3 signals much of the time, not always), and thyroid’s binding protein (TBG).
But even these tests can miss subclinical hypothyroidism that lurks in many, due to so many endocrine disruptors in air, food and water altering thyroid receptor functioning. These disrupt the thyroid receptor (as well as other receptors from sex steroids, to insulin, and more that is why they are labeled “disruptors”).
I have interviewed Barbara Demeneix, a French scientist, and her theories that common pollutants are damaging thyroid functioning in up towards 80% of humans.
Dr. Brownstein, a world expert in thyroid disease, has written books on this, too. I have interviewed him extensively, also.