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.

Standard Treatment for Underactive Thyroid Gland Still Best

A expert panel reviewing treatments for hypothyroidism has concluded that the drug levothyroxine (L-T4) should remain the standard of care.

The updated guidelines from the American Thyroid Association were published recently in the journal Thyroid.

The thyroid gland produces hormones that control the way every cell in the body uses energy. For example, thyroid hormones control how fast you burn calories and how fast your heart beats. If the thyroid gland produces too little thyroid hormone to control these activities the condition is called hypothyroidism.

A task force convened by the thyroid association reviewed available medical literature and found no evidence that other types of thyroid hormone replacements are better than L-T4, which has long been the standard of care for patients with hypothyroidism. Brand names for L-T4 include Synthroid and Levoxyl.

However, while L-T4 is effective in most patients, some do not regain ideal health when taking L-T4 alone, the authors noted.

The guidelines “provide useful, up-to-date information on why to treat, including subclinical disease, who to treat, and how to treat hypothyroidism,” Dr. Hossein Gharib, president of the thyroid association, said in a journal news release.

“Information is evidence-based and recommendations are graded. I think they will be used extensively by all clinical endocrinologists, especially by our members,” added Gharib, a professor of medicine at the Mayo Clinic College of Medicine in Rochester, Minn.