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New standard falls short: subclinical hyperthyroidism guideline.

BOSTON -- Some patients who fit the latest definition of subclinical hyperthyroidism may not have the condition and probably should not be treated, according to Dr. David S. Cooper of Johns Hopkins University in Baltimore.

"How low does the [thyroid stimulating hormone] have to go, and does low TSH always mean subclinical hyperthyroidism?" he asked rhetorically at the annual meeting of the American Association of Clinical Endocrinologists. "There is currently no answer to that question."

Nonetheless, Dr. Cooper, director of the endocrinology division at Sinai Hospital of Baltimore, described the new standard as a "reasonable cut-off" in the absence of clinical trials evaluating the benefits of treatment.

The guideline came out of a consensus conference organized by the American Association of Clinical Endocrinologists, the Endocrine Society, and the American Thyroid Association after various professional groups found that they could not make a recommendation. The conference defined subclinical hyperthyroidism as serum TSH levels below 0.1 mU/L when serum free [T.sub.4] and [T.sub.3] levels are normal and the patient has no symptoms or history of thyroid disease.

One problem with the standard is that normal TSH and the "set point" for subclinical hyperthyroidism may become lower with age, Dr. Cooper said.

"There are some people, particularly older people, who may have an altered set point," he said, citing an Italian study that reported TSH levels below 0.09 mU/L in 10% of healthy centenarians (J. Clin. Endocrinol. Metab. 77[5]:1130-34, 1993).

The name "subclinical hyperthyroidism" also may be a misnomer, he said, suggesting that "mild hyperthyroidism" might be more accurate in patients with mild symptoms of thyroid disease. Even the dividing line between "younger" and "older" patients is not clearly established, he said, after offering his own proposal for when to treat the condition.

For older patients with a TSH level below 0.1, he suggested treatment if the patient also has osteoporosis, symptoms of thyroid disease, heart disease, goiter, or thyroid function tests in the upper range of normal. With the same comorbidities, however, he said he would not treat younger patients with thyroid levels between 0.1 mU/L and 0.5 mU/L.
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Title Annotation:Clinical Rounds
Author:MacNeil, Jane Salodof
Publication:OB GYN News
Date:Jul 15, 2004
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