A patient with subclinical hypothyroidism has a very high thyroid-stimulating hormone (TSH), but his other thyroid function tests (triiodothyronine, thyroxine, etc.) are normal. His insurer will not pay for testing more often than twice a year. Is retesting the TSH alone sufficient for adjusting levothyroxine doses?
—Ferdinand M. Rivera, MD, Salinas, P.R.

Subclinical hypothyroidism is a laboratory diagnosis in which the TSH is above the upper limit of normal and the serum-free thyroxine is within the normal range. The fundamental question is whether these patients should be treated with levothyroxine. This is a very controversial area, and the evidence does not yet provide clear answers. Benefits of treatment include preventing progression to overt hypothyroidism and amelioration of nonspecific symptoms of hypothyroidism, as well as improving the lipid profile and possibly helping cardiac contractility. Arguments against treatment include expense and the likelihood that some patients are not benefiting and that the risks of overtreatment may outweigh the possible benefits.

A group of endocrinologists in 2004 recommended treating patients with subclinical hypothyroidism and a TSH >10 mIU/L in order to prevent progression to overt hypothyroidism and provide possible cardiac and lipid benefits (JAMA. 2004;291:228-238). They recommended against treating patients with subclinical hypothyroidism and a TSH <10 mIU/L and suggested repeating the thyroid function tests at 6- to 12-month intervals. Some patients with a TSH <10 have symptoms compatible with hypothyroidism, and the panel does allow for consideration of a levothyroxine trial while monitoring for symptomatic benefit.

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However, they qualify this recommendation by stating that the likelihood of improvement is small and there is insufficient evidence to expect benefits (beyond those with placebo) in this group. These general recommendations do not include pregnant women, who deserve special consideration and a lower threshold for treatment since hypothyroidism can adversely affect intellectual performance in the child. If the decision is made to treat a patient with levothyroxine, the TSH is adequate for monitoring and can be measured four to six weeks after beginning therapy, after any change in dose, and then annually once the levels are found to be stable.
—Susan Kashaf, MD, MPH (117-22)