When to adjust thyroid hormone dosing

When a patient's thyroid-stimulating hormone (TSH) is elevated, should I hold off prescribing thyroid-hormone replacement therapy until the free thyroxine (T4) level falls below the lower limit of normal?
—LOUIS H. MCCORMICK, MD, Franklin, La.

The clinical scenario in which a patient's TSH is above normal but his T4 remains within normal limits is often referred to as subclinical hypothyroidism, or a more mild form of the hypothyroid spectrum. These patients may have vague complaints along the classic hypothyroid spectrum. Justification for treatment often rests on somewhat controversial data regarding the ultimate evolution of overt hypothyroidism, negative consequences on serum lipids and cardiovascular health, and possible subtle detrimental cognitive effects. Treatment in this case focuses more on the level of TSH than on the level of T4.

David S. Cooper has published an excellent clinical review and treatment algorithm on this subject (N Engl J Med. 2001;345:260-265. Available at content.nejm.org/cgi/content/full/345/4/260. Accessed June 12, 2009). This algorithm proposes measurement of a full thyroid profile, antibodies against thyroperoxidase, and lipids. If the patient has antibodies against thyroperoxidase or a TSH >10 mU/L, then thyroxine therapy is recommended. If the patient's TSH is <10, then symptoms, a goiter, elevated lipids, or ovulatory dysfunction might prompt treatment. Another expert panel recommends treatment in all patients with a TSH >10 with the goal of therapy being to normalize the level of TSH (JAMA. 2004;291:228-238. Available at jama.ama-assn.org/cgi/content/full/291/2/228. Accessed June 12, 2009).
Christopher Ruser, MD (129-2)
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