Repeated thyroid function evaluations in the dog: a retrospective study of 8,309 dogs

Area of Science:

• Veterinary Medicine
• Canine Endocrinology
• Immunology

Background:

• Hypothyroidism is a common endocrine disorder in dogs, with certain breeds predisposed.
• Autoimmune thyroiditis, a frequent cause of hypothyroidism, has a genetic basis.
• Breeders seek methods to decrease the incidence of inherited canine thyroid disease.

Purpose of the Study:

• To evaluate the stability of thyroid function test results over time in dogs.
• To determine if thyroglobulin autoantibody (TgAA) levels change, impacting diagnosis.
• To inform breeding strategies by assessing the reliability of phenotypic testing.

Main Methods:

• Retrospective analysis of data from the Orthopedic Foundation for Animals (OFA) database.
• Inclusion of 8,309 dogs with at least two thyroid assessments.
• Comparison of initial thyroid hormone and TgAA classifications with subsequent evaluations.

Main Results:

• Over 90% of dogs initially classified as normal for thyroid function maintained normal status in follow-up.
• Dogs initially classified as equivocal showed the most significant diagnostic changes.
• A portion of dogs diagnosed with compensative autoimmune thyroiditis later reverted to normal, while half remained diagnosed.

Conclusions:

• Transient low-level autoantibody presence may occur, necessitating reevaluation.
• Phenotypic testing for canine thyroid function can change over time.
• Repeated assessment is crucial for confirming autoimmune thyroiditis in dogs with autoantibodies.