It´s often said that T4 to T3 conversion is normal in thyroid patients as most of it takes place outside the thyroid gland; I´ve read that the total daily output of T3 from the gland is ca 10 mcg - half of it produced directly by the gland and half of it coming from conversion taking place inside the gland itself. So the rest - depending on source, the total daily amount of T3 needed by the body is 30-50 mcg - comes from extra-thyroidal conversion, mostly in the liver, but also in the kidneys and gut.
But Paul Robinson writes in "The Thyroid Patient´s Manual" (p. 142): "If you have lost thyroid tissue through a thyroidectomy or through Hashimoto´s thyroiditis, you will also have lost a substantial amount of T4 to T3 production. The thyroid gland converts more T4 than any other tissue".
He suggests this argument is used to convince doctors to prescribe T3.
Any thoughts?