Thyroid Research Thyroid Research Archive Thyroid Disease
The background of the study. Subclinical hypothyroidism and subclinical hyperthyroidism are defined, respectively, as high or low serum thyrotropin (TSH) concentrations and normal serum free thyroxine (T4) concentrations, independent of symptoms of thyroid dysfunction. Whether patients with these disorders have problems and benefit from therapy is debated.
How the study was done. The literature on subclinical hypothyroidism and subclinical hyperthyroidism was reviewed by a panel of experts in endocrinology, epidemiology, and preventive health services. The panel rated the strength of the information about the health effects and benefits of therapy of the two disorders as good, fair, or insufficient.
The results of the study. The prevalence of subclinical hypothyroidism was estimated to range from 4 to 8.5 percent among adults in the United States. The panel found reasonable evidence that subclinical hypothyroidism can progress to overt hypothyroidism (high serum TSH and low free T4 concentrations) and that this progression can be prevented by T4 therapy. The panel concluded that there is little evidence that subclinical hypothyroidism is associated with symptoms of hypothyroidism, cardiac dysfunction, or hypercholesterolemia, or that T4 therapy is beneficial.
The prevalence of subclinical hyperthyroidism was estimated to be 3.2 percent. The panel found reasonable evidence that subclinical hyperthyroidism can progress to overt hyperthyroidism (low serum TSH and high free T4 concentrations). The panel concluded that marked (but not mild) subclinical hyperthyroidism is a risk factor for atrial fibrillation (a cardiac rhythm disorder) and low bone density, but that there is insufficient or no evidence to conclude that it is associated with symptoms of hyperthyroidism or cardiac dysfunction, or that these problems can be reversed or prevented by antithyroid therapy.
The conclusions of the study. There is little evidence that patients with subclinical hypothyroidism or subclinical hyperthyroidism have any manifestations of thyroid dysfunction or benefit from therapy. Population-based screening for these disorders is not indicated.
The original article. Surks MI, Ortiz E, Daniels GH, Sawin CT, Col NF, Cobin RH, Franklyn JA, Hershman JM, Burman KD, Denke MA, Gorman C, Cooper RS, Weissman NJ. Subclinical thyroid disease: scientific review and guidelines for diagnosis and management. JAMA 2004;291:228-38.