Serum thyroxine content before and after thyrotropin stimulation in dogs with suspected hypothyroidism

Thyroid function in 39 dogs was studied, utilizing serum thyroxine (T-4) analysis before and 10 hours after thyroid-stimulating hormone (TSH) stimulation. All dogs were treated with pharmacologic doses of L-thyroxine or liothyronine, and the dogs' responses to these treatments were documented. Failure to double control T-4 values after TSH administration was associated with a good response to thyroid medication, whereas a doubling of the control values after TSH administration was associated with negative responses to thyroid medication. Significant difference was not found in the control T-4 values of the various groups, whereas the post-TSH values were significantly different. The study substantiated the value of TSH-response tests in the presumptive diagnosis of canine hypothyroidism.