Comparison of thyroperoxidase and microsomal antibody assays in sera from patients with Graves disease

Anti-microsomal (anti-Mic Ab) and anti-thyroperoxidase antibody activities (anti-TPO Ab) were compared by using commercially available radioassay kits. Sera were collected from 52 patients with Graves disease before and after administration of carbimazole (1-methyl-2-thio-3-carbethoxyimidazole). The two antibody concentrations were significantly correlated, both before treatment (r = 0.835, P less than 0.001, n = 52) and at the end of treatment (r = 0.584, P less than 0.001, n = 52). Twenty-nine (Group I) of the 52 patients were in remission for two years after drug withdrawal, whereas 23 (Group II) relapsed. Within each group, the anti-Mic and anti-TPO Ab concentrations were significantly correlated (Group I: r = 0.781, P less than 0.0001; Group II: r = 0.866, P less than 0.0001). Relapse vs nonrelapse was linked to the antibody positivities measured before treatment: 91% vs 65% (chi 2 = 4.75, P less than 0.02) for anti-Mic Ab and 87% vs 62% (chi 2 = 4.05, P less than 0.02) for anti-TPO Ab. We conclude that assays of anti-Mic and anti-TPO Ab are equally reliable analytically and equally informative clinically. Because of its rapid implementation, the anti-TPO assay may advantageously replace anti-Mic Ab assay, especially for forming a prognosis of Graves disease.