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.