Differentiation Between Dogs With Primary Hypothyroidism and Dogs With Non Thyroidal Illness Based On Plasma Concentrations of Growth Hormone with a TSH Releasing Hormone Stimulation Test

Primary hypothyroidism is one of the most common endocrine disorders in dogs. In most dogs with primary hypothyroidism plasma concentrations of total thyroxin (TT4) and total triiodothyronine (TT3) are below their respective reference range. However, these thyroid hormone concentrations may also be low in dogs with a normal thyroid function due to non-thyroid illness (NTI) or drugs. Consequently, the plasma thyroid stimulating hormone (TSH) concentration should be measured when TT4 is below its reference range. When the plasma TSH concentration is clearly above the upper limit
of the reference range the dog has primary hypothyroidism. However when the TSH plasma concentration is within the reference range, the dog may still have primary hypothyroidism. When a low TT4 in combination with a normal cTSH has been found, the dog could undergo a biopsy of the thyroid gland or scintigraphy of the thyroid glands. […]