Prevalence of serum thyroid hormone autoantibodies in dogs with clinical signs of hypothyroidism

OBJECTIVE: To determine prevalence of thyroid hormone autoantibodies (THAA) in serum of dogs with clinical signs of hypothyroidism. DESIGN: Cohort study. SAMPLE POPULATION: 287,948 serum samples from dogs with clinical signs consistent with hypothyroidism. PROCEDURE: Serum THAA were detected by use of a radiometric assay. Correlation and chi2 analyses were used to determine whether prevalence varied with breed, age, sex, or body weight. Only breeds for which > or = 50 samples had been submitted were used for analysis of breed prevalence. RESULTS: Thyroid hormone autoantibodies were detected in 18,135 (6.3%) samples. The 10 breeds with the highest prevalence of THAA were the Pointer, English Setter, English Pointer, Skye Terrier, German Wirehaired Pointer, Old English Sheepdog, Boxer, Maltese, Kuvasz, and Petit Basset Griffon Vendeen. Prevalence was significantly correlated with body weight and was highest in dogs between 2 and 4 years old. Females were significantly more likely to have THAA than were males. CONCLUSIONS AND CLINICAL RELEVANCE: Thyroid hormone autoantibodies may falsely increase measured triiodothyronine (T3) and thyroxine (T4) concentrations in dogs; results suggest that T3 concentration may be falsely increased in approximately 57 of 1,000 dogs with hypothyroidism and that T4 concentration may be falsely increased in approximately 17 of 1,000 dogs with hypothyroidism. Results also suggested that dogs of certain breeds were significantly more or less likely to have THAA than were dogs in general.