title: Free thyroxine concentrations by equilibrium dialysis and chemiluminescent immunoassays in 13 hypothyroid dogs positive for thyroglobulin antibody.
abstract: 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).
  
  
  METHODS
  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 < .0001 for FT4h and P < .001for FT4v) higher than the hypothesized false-negative rate of 0%.
  
  
  CONCLUSIONS
  Caution should be exercised in screening dogs for hypothyroidism using FT4 measured by CLIA alone. Some (25-38%) TGA-positive hypothyroid dogs had FT4 concentrations determined by CLIA that did not support a diagnosis of hypothyroidism.
authors: Department of Clinical Sciences, College of Veterinary Medicine, Cornell University, Ithaca, NY, 14853.
authors: J F
authors: JF
authors: Randolph
authors: The New York State Veterinary Diagnostic Endocrinology Laboratory, Animal Health Diagnostic Center, College of Veterinary Medicine, Cornell University, Ithaca, NY, 14853.
authors: S V
authors: SV
authors: Lamb
authors: The New York State Veterinary Diagnostic Endocrinology Laboratory, Animal Health Diagnostic Center, College of Veterinary Medicine, Cornell University, Ithaca, NY, 14853.
authors: J L
authors: JL
authors: Cheraskin
authors: The New York State Veterinary Diagnostic Endocrinology Laboratory, Animal Health Diagnostic Center, College of Veterinary Medicine, Cornell University, Ithaca, NY, 14853.
authors: B J
authors: BJ
authors: Schanbacher
authors: The New York State Veterinary Diagnostic Endocrinology Laboratory, Animal Health Diagnostic Center, College of Veterinary Medicine, Cornell University, Ithaca, NY, 14853.
authors: V J
authors: VJ
authors: Salerno
authors: The New York State Veterinary Diagnostic Endocrinology Laboratory, Animal Health Diagnostic Center, College of Veterinary Medicine, Cornell University, Ithaca, NY, 14853.
authors: K M
authors: KM
authors: Mack
authors: Department of Population Medicine & Diagnostic Sciences, College of Veterinary Medicine, Cornell University, Ithaca, NY, 14853.
authors: J M
authors: JM
authors: Scarlett
authors: Department of Population Medicine & Diagnostic Sciences, College of Veterinary Medicine, Cornell University, Ithaca, NY, 14853.|The New York State Veterinary Diagnostic Endocrinology Laboratory, Animal Health Diagnostic Center, College of Veterinary Medicine, Cornell University, Ithaca, NY, 14853.
authors: N J
authors: NJ
authors: Place
mesh_terms: D000818:Animals; D001323:Autoantibodies / Q000276:immunology*; D004283:Dog Diseases / Q000097:blood* / Q000175:diagnosis / Q000276:immunology; D004285:Dogs; D004797:Enzyme-Linked Immunosorbent Assay / Q000662:veterinary; D005189:False Positive Reactions; D005260:Female; D050031:Hashimoto Disease / Q000097:blood / Q000175:diagnosis / Q000276:immunology / Q000662:veterinary; D007037:Hypothyroidism / Q000097:blood / Q000175:diagnosis / Q000276:immunology / Q000662:veterinary*; D008163:Luminescent Measurements / Q000379:methods / Q000662:veterinary*; D008297:Male; D013954:Thyroglobulin / Q000276:immunology*; D013967:Thyroiditis, Autoimmune / Q000097:blood / Q000175:diagnosis / Q000276:immunology / Q000662:veterinary; D013972:Thyrotropin / Q000097:blood; D013974:Thyroxine / Q000097:blood*; D014284:Triiodothyronine / Q000097:blood
chemical_list: D001323:Autoantibodies; D014284:Triiodothyronine; D013972:Thyrotropin; D013954:Thyroglobulin; D013974:Thyroxine
keywords: FT4; TGAA; chemiluminescence; hypothyroidism