Usefulness of a chromatographic method to detect circulating antithyroid hormone autoantibodies in canine serum.

Antithyroid hormone autoantibodies (THBA), described in both humans and 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 present 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 incubation of samples with 125I-T3 and 125I-T4 in presence of 8-anilino-1-naphtalenesulfonic acid, samples were eluted and radioactivity values counted. Eluate radioactivity values > 10% and > 30% were considered positive for THBA presence for antiT3 and antiT4 detection, respectively. High radioactivity values were detected in dog serum 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, with species specific differences in thyroid hormone metabolism; thus, taking into account the rarely availability of canine serum TSH and anti-thyroglobulin antibody immunoassay detection methods, it was possible to correctly diagnose the hypothyroidism in a dog with apparently extremely high values of thyroid hormones due to THBA interference.