Development and validation of an improved enzyme-linked immunosorbent assay for the detection of thyroglobulin autoantibodies in canine serum samples

An enzyme-linked immunosorbent assay to detect thyroglobulin autoantibodies (TGAB) in canine serum was developed and validated. The test result for ea ch sample was derived from the optical density readings (OD) and expressed as an Ab-score(%) calculated from three in-house calibrators. The assay spe cifically detected TGAB as judged from lack of response in the assay after samples had been incubated with specific antigen. Intra- and interassay coe fficients of variation ranged from 2.0-4.9% and 4.6-9.9%, respectively. The detection limit, an Ab-score of 5.6%, was close to the median Ab-score of 10% observed in healthy dogs (n = 132). The median Ab-score of dogs with pr imary hypothyroidism and lymphocytic thyroiditis (n = 11), skin diseases (n = 35), and non-thyroidal diseases (n = 63) was 340%, 12%, and 8%, respecti vely. The prevalence of TGAB in hypothyroid dogs with lymphocytic thyroidit is (sensitivity) was 91% (95% confidence limits: 59%-99%). In dogs with der matological diseases without lymphocytic thyroiditis the prevalence of TGAB was 3% corresponding to a specificity of 97% (95% confidence limit: 85%-10 0%). In dogs with non-thyroidal diseases and healthy dogs the prevalence of TGAB was 5% and 6%, respectively. The diagnostic accuracy of serum TGAB wa s evaluated by subjecting the data from ii dogs with lymphocytic thyroiditi s and 35 control dogs without lymphocytic thyroiditis to receiver-operating characteristic curve analysis. The area under the receiver-operating chara cteristic curve (W = 0.966; 95% confidence limit 87%-100%) was significantl y higher than that of a worthless test (0.5) (P < 0.0001), thereby indicati ng that serum TGAB measurements distinguished between dogs with and without lymphocytic thyroiditis. (C) Elsevier Science Inc. 1998.