Prevalence of anti-thyroid peroxidase antibodies in serum in the elderly: comparison with other tests for anti-thyroid antibodies.

Autoimmune thyroid disease, especially chronic thyroiditis, is prevalent in elderly women and is probably the major cause of hypothyroidism in this population. The reported prevalence of chronic thyroiditis is variable, depending on the area of residence and the method(s) used to detect the presence of anti-thyroid antibodies. The recent finding that thyroid peroxidase (TPO) is the antigen for the thyroid anti-microsomal antibody (AbM) has resulted in the development of sensitive radioimmunoassays (RIA) to detect the presence of AbTPO. We have determined the prevalence of AbTPO (by RIA) in sera from 342 elderly subjects, 248 women and 94 men (mean age 80 years) residing in Reggio Emilia, Italy, and compared the results with other methods for detecting anti-thyroid antibodies, including anti-thyroglobulin (AbTg) and AbM measured by passive hemagglutination (PH) of tanned erythrocytes, and AbM measured by RIA. The prevalence of positive AbTPO was 2.3% in the men and 10.2% in the women, only slightly higher than the prevalence of AbM. However, in the antibody-positive sera, the mean value for AbTPO was approximately 20-fold greater than the upper limit of the normal range, whereas the mean value for AbM was only threefold greater. The prevalence of positive titers for AbM and AbTg measured by PH was far lower, 1.2% and 3.2%, respectively, and those sera weakly positive for AbM and AbTg by PH were strongly positive for AbTPO by RIA. AbTPO RIA may be more useful than AbM and AbTg hemagglutination and AbM RIA for detecting the presence of autoimmune thyroid disease.