ANTITHYROID PEROXIDASE (ANTI-TPO) ANTIBODIES IN THYROID-DISEASES, NONTHYROIDAL ILLNESS AND CONTROLS - CLINICAL VALIDITY OF A NEW COMMERCIALMETHOD FOR DETECTION OF ANTI-TPO (THYROID MICROSOMAL) AUTOANTIBODIES

The identification of the thyroid peroxidase (TPO) as the main antigen of the thyroid microsomal fraction has enabled the development of a s ensitive and specific assay for detection of the corresponding autoant ibodies. We evaluated the diagnostic validity of the anti-TPO assay in 303 patients with different types of thyroid disease and in controls. Clearly elevated anti-TPO values (anti-TPO > 500 units/ml) were found in 59% of patients with thyroiditis but in none of the controls or th e patients with non-thyroidal illness. The mean anti-TPO levels in the se two control groups were 26 +/- 31 units/ml (mean +/- S.D.) and 39 /- 34 units/ml, respectively. The highest frequency of positive result s (88%) was obtained in patients with autoimmune hypothyroidism (clini cal diagnosis: Hashimoto's thyroiditis) followed by patients with Grav es' disease (53%). With a cut-off point of 200 units/ml, a sensitivity of 96% was obtained for Hashimoto's thyroiditis and of 59% for Graves ' disease with a specificity of 100% (50 cases). The new method (anti- TPO, Dynotest) was compared with three conventional methods (35 sample s). The results for all measurements were in general agreement. In two cases the results were clearly discordant: one sample contained high anti-thyroglobulin antibody concentrations, the other was obtained fro m a patient with non-thyroidal illness. In both instances the 'classic al' assays yielded false-positive results. Treatment of autoimmune hyp erthyroidism resulted in a median decrease in anti-TPO levels of over 50% after reaching the euthyroid state (P < 0.05), whereas in persiste nt hyperthyroidism no consistent changes were observed. In autoimmune hypothyroidism a marked variability in anti-TPO levels was noted. Some patients showed a clear decrease in anti-TPO levels during T4 substit ution whereas in others no consistent changes were observed.