Vol. 7, Issue 2, Part A (2025)

Thyroid disorders represent some of the most common endocrine diseases in companion animals, especially dogs and cats. It is focuses on the physiology of the thyroid gland, mechanisms of thyroid hormone synthesis, regulation, metabolism, and the diverse diagnostic approaches used to assess thyroid function in veterinary practice. The thyroid gland produces the hormones thyroxine (T₄) and triiodothyronine (T₃), which play essential roles in metabolism, growth, neurological development, cardiac function, and thermoregulation. Their secretion is controlled by a tightly regulated feedback loop involving hypothalamic TRH and pituitary TSH.

Accurate assessment of thyroid status requires measuring total and free hormone concentrations (tT₄, fT₄, tT₃, fT₃), as well as evaluating TSH levels through immunoassays. Various factors including circadian rhythm, sample handling, medications, autoantibodies, breed differences, and concurrent non-thyroidal illness may influence hormone values, complicating interpretation. Detection of autoantibodies (TgAA, T₄AA, T₃AA, and TpAA) is important for identifying autoimmune thyroiditis, a major cause of primary hypothyroidism in dogs.