Comparison of thyrotropin-releasing hormone (TRH) to thyrotropin (TSH) stimulation for evaluating thyroid function in dogs

Five normal dogs and 22 dogs with dermatological signs suggestive of hypothyroidism were evaluated using thyrotropin-releasing hormone (TRH) and thyrotropin (TSH) stimulation. Thyroxine (T4) concentration after TRH stimulation was significantly lower than that obtained by TSH stimulation. It was not possible to identify hypothyroid dogs with the TRH-stimulation test, because some euthyroid dogs had either decreases in T4 or only slight increases in T4 concentrations after TRH stimulation. In addition, dogs with pyoderma had decreased responses in serum T4 after TRH stimulation, which became normal following treatment with antibiotics. Six of the 22 dogs were diagnosed as hypothyroid based on TSH results and responses to thyroid hormone replacement. It was concluded that TRH stimulation is not a useful means of diagnosing hypothyroidism in dogs.