The TSH (thyroid stimulating hormone) is the gold standard for evaluating thyroid health. TSH is a pituitary hormone that directs the thyroid to make T4. The normal lab range is 0.4 – 4.5 ulU/L. However, the functional range is much narrower from 1-2 ulU/L. This functional range has been recommended by the American Board of Endocrinology since 2003, but has been ignored by most physicians.
As a minimum, I also recommend running a T3 and T4. Approximately 97% of the thyroid hormone produced by the thyroid gland is in the form of T4. This is the inactive, stable form that circulates in your blood stream. It is called T4 because it is a cholesterol ring with four molecules of iodine attached to it.
When the body’s basic metabolism requires stimulation, the liver removes one molecule of iodine from T4 making T3, the active form of thyroid hormone. This is under the direction of the adrenal glands which take their orders from the hypothalamus and pituitary (home of TSH).
Most thyroid issues are related to poor conversion of T4 to T3, so including these tests when evaluating the thyroid is a must.
Under high levels of stress, the liver can remove the wrong iodine molecule creating ‘reverse T3’. It is indistinguishable from normal T3 and must be measured directly. This is a common occurrence in American Indians and those of Irish decent. Reverse T3 does not have any metabolic function and appears to be a safety valve when stress levels are so high that excess T3 might be released from the liver. Again, this test is seldom run in traditional medical practices.
