Free Thyroxine Concentrations by Equilibrium Dialysis and Chemiluminescent Immunoassays in 13 Hypothyroid Dogs Positive for Thyroglobulin Antibody

• Published in: Journal of veterinary internal medicine 2015-05, Vol.29 (3), p.877-881
• Main Authors: Randolph, J.F., Lamb, S.V., Cheraskin, J.L., Schanbacher, B.J., Salerno, V.J., Mack, K.M., Scarlett, J.M., Place, N.J.
• Format: Article
• Language: English
• Subjects: Animals; Autoantibodies - immunology; Automation; Chemiluminescence; Diagnosis; Dog Diseases - blood; Dog Diseases - diagnosis; Dog Diseases - immunology; Dogs; Endocrinology; Enzyme-Linked Immunosorbent Assay - veterinary; Enzymes; Equilibrium; Equilibrium dialysis; False Positive Reactions; Female; FT4; Hashimoto Disease - blood; Hashimoto Disease - diagnosis; Hashimoto Disease - immunology; Hashimoto Disease - veterinary; Hemodialysis; Hypothyroidism; Hypothyroidism - blood; Hypothyroidism - diagnosis; Hypothyroidism - immunology; Hypothyroidism - veterinary; Immunoassay; Immunoassays; Immunoglobulins; Laboratories; Luminescent Measurements - methods; Luminescent Measurements - veterinary; Male; Radioimmunoassay; TGAA; Thyroglobulin; Thyroglobulin - immunology; Thyroid gland; Thyroid hormones; Thyroiditis, Autoimmune - blood; Thyroiditis, Autoimmune - diagnosis; Thyroiditis, Autoimmune - immunology; Thyroiditis, Autoimmune - veterinary; Thyrotropin - blood; Thyroxine; Thyroxine - blood; Triiodothyronine; Triiodothyronine - blood; Veterinary medicine
• ISSN: 0891-6640; 1939-1676
• DOI: 10.1111/jvim.12573

Objective To determine if concentrations of free thyroxine (FT4) measured by semi‐automated chemiluminescent immunoassay (CLIA) correspond to FT4 determined by equilibrium dialysis (ED) in hypothyroid dogs positive for thyroglobulin antibody (TGA). Animals Thirteen TGA‐positive dogs classified as hypothyroid based on subnormal FT4 concentrations by ED. Methods Qualitative assessment of canine TGA was performed using an enzyme‐linked immunosorbent assay. Serum total thyroxine and total triiodothyronine concentrations were measured by radioimmunoassay. Serum FT4 concentration was determined by ED, and also by semi‐automated CLIA for human FT4 (FT4h) and veterinary FT4 (FT4v). Canine thyroid stimulating hormone concentration was measured by semi‐automated CLIA. Results Each dog's comprehensive thyroid profile supported a diagnosis of hypothyroidism. For detection of hypothyroidism, sensitivities of CLIA for FT4h and FT4v were 62% (95% CI, 32–85%) and 75% (95% CI, 36–96%), respectively, compared to FT4 by ED. Five of 13 (38%) dogs had FT4h and 2 of 8 (25%) dogs had FT4v concentrations by CLIA that were increased or within the reference range. Percentage of false‐negative test results for FT4 by CLIA compared to ED was significantly (P