USEFULNESS OF A CHROMATOGRAPHIC METHOD TO DETECT CIRCULATING ANTITHYROID HORMONE AUTOANTIBODIES IN CANINE SERUM

Antithyroid hormone autoantibodies (THBA), described in both humans an d animals, result in variable interference when thyroid hormone plasma levels are measured by immunoassays. We previously described a quick chromatographic method to detect circulating THBA in humans. In the pr esent experience, we applied the method on canine sera (10 normal dogs and 3 dogs affected by hypothyroidism) to detect the THBA presence in a dog (no. 13) with clinical evidence of hypothyroidism, in spite of apparently extremely high values of thyroid hormone. After a short inc ubation of samples with I-125-T3 and (125)1-T4 in presence of 8-anilin o-1-naphtalenesulfonic acid, samples were eluted and radioactivity val ues counted. Eluate radioactivity values >10% and >30% were considered positive for THBA presence for antiT3 and antiT4 detection, respectiv ely. High radioactivity values were detected in dog serun no. 13 and, therefore, it was considered positive for THBA presence. The Scatchard plot analysis revealed the presence of a monoclonal autoantibody with the highest affinity for T3 and an additional tenfold lower affinity for T4. In conclusion, our chromatographic method allows the detection and the characterization of THBA in species different from humans, wi th species specific differences in thyroid hormone metabolism; thus, t aking into account the rarely availability of canine serum TSH and ant i-thyroglobulin antibody immunoassay detection methods, it was possibl e to correctly diagnose the hypothyroidism in a dog with apparently ex tremely high values of thyroid hormones due to THBA interference. (C) 1996, Editrice Kurtis.