Wednesday, December 14, 2016
Wisdom Wednesday: The Thyroid Profile
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.
Next are the thyroid autoantibodies and TPO (thyroid peroxidase). These tests look for autoimmune attack against the thyroid. When positive, they indicate Hashimoto’s thyroiditis. However, the antibodies can be transient and don’t always show on laboratory testing. Further, there is no traditional medical treatment for Hashimoto’s thyroiditis other than exogenous thyroid hormone therapy so again, these tests are seldom run. It is estimated that fully a third of patients diagnosed with hypothyroidism actually are suffering from Hashimoto’s thyroiditis and remain undiagnosed. Clinically, I think it’s closer to half than a third.
Finally, the THBG (thyroid hormone binding globulin) measures how much of the circulating hormone is bound up by the protein goblulin. Excess THBG can occur in hypothyroidism and other diseases, including excess estrogen. A deficiency of THBG can occur in hyperthyroidism and liver disease.
The Bottom Line:
When evaluating the thyroid, running just the TSH is inadequate. You must at least include the T3 and T4. However, if autoimmune disease is suspected, the thyroid autoantibodies and TPO must be included. If Wilson’s disease or ethnicity is a concern, add the reverse T3. Finally, if looking at other hormonal imbalance then add the THBG.