Sampling protocol for thyrotropin stimulation test in the dog.

A study was designed to assess the secretory response of thyroid glands in dogs to small doses of thyrotropin (thyroid-stimulating hormone, TSH; 2.5 and 5.0 units, total IV dose), and to establish valid blood-sampling periods in cases in which thyroxine concentrations were different from base-line values. Significant (P less than 0.001) response occurred as early as 3 hours after TSH administration, with peak response at 5 to 7 hours. Fasting dogs for 12 hours had no effect on test results. Because base-line thyroxine concentrations in dogs are equivocal and base-line triiodothyronine concentrations are influenced by many factors, thyrotropin stimulation testing is one of the best methods at present to evaluate thyroid function. Administration of a total dose of 2.5 to 5.0 units of TSH is economical, and collection of the 2nd blood sample as early as 3 hours for response may be advantageous in terms of scheduling for the client and practicing veterinarian.