The aging thyroid. Relationship between elevated serum thyrotropin level and thyroid antibodies in elderly patients.

The relationship of thyroid antibodies and the serum level of thyrotropin in older adults (over age 60) was studied to determine whether thyroid antibodies were a good clue to thyroid failure in elderly persons. Of those with thyroid failure, evidenced by clearly elevated serum thyrotropin values (more than 10 microU/ml), 67 percent had positive antimicrosomal antibody levels, a prevalence much greater (p less than 0.001) than that among those of comparable age with normal thyroid function (18 percent). Nevertheless, one third (33 percent) had thyroid failure without positive antimicrosomal antibody levels; this was true whether or not a low serum thyroxine value was present. Furthermore, of those with positive antimicrosomal antibody levels, most (68 percent) did not have thyroid failure. Thus, although positive antimicrosomal antibody levels occurred more often in elderly patients with thyroid failure than in those with normal thyroid function, a sizable fraction of those with thyroid failure did not have positive antimicrosomal antibody levels. Hence, measurement of thyroid antimicrosomal antibodies is not a good test of early thyroid failure in older patients; direct demonstration of a clearly elevated serum thyrotropin value is a better approach.