Use of recombinant human thyroid-stimulating hormone for thyrotropin stimulation test in healthy, hypothyroid and euthyroid sick dogs

Recombinant human thyroid-stimulating hormone (rhTSH) was evaluated for the diagnosis of canine hypothyroidism, using TSH response tests. Phase I stimulation tests were performed in 6 healthy dogs weighing over 20 kg, using 50 and then 100 μg of freshly reconstituted rhTSH administered intravenously. In phase II, the same dogs were stimulated by using 100 μg of rhTSH frozen for 3 months at −20°C. Phase III stimulation tests were performed by using 50 or 100 μg of freshly reconstituted or frozen rhTSH in healthy (n = 14), euthyroid sick (n = 11) and hypothyroid dogs (n = 9). A dose of 100 μg of rhTSH was judged more appropriate for dogs weighing more than 20 kg. Biological activity of rhTSH after freezing at −20°C for up to 12 weeks was maintained. When stimulated, significant (P < 0.05) increases in total thyroxine concentration were observed only in healthy and euthyroid sick dogs. Results of this study show that the rhTSH stimulation test is able to differentiate euthyroidism from hypothyroidism in dogs.