SPECIFIC MEASUREMENT OF CANINE TSH FOR DI AGNOSIS OF HYPOTHYROIDISM IN THE DOG

The present paper describes our first experiences with new assay syste ms for the specific measurement of canine TSH. Eighteen healthy beagle dogs had frequent blood samples taken including repeated TRH-tests. A total of 855 patients with suspected thyroid disorders had blood samp les analysed, including 103 TRH-tests. All samples were analysed for t he cTSH and T-4, selected samples were assayed for prolactin. Both the immunoradiometric assay (TSH-IRMA) and the enzyme immunoassay (TSH-EI A) proved to be reliable and reproducible assay systems, the latter af ter some initial problems. TRH stimulated TSH release in the majority of cases. Ten patients with primary hypothyroidism had clearly elevate d TSH values as expected. However our results show an array of hormona l patterns not always as expected: The elevated TSH-levels of the 10 h ypothyroid patients could not be further stimulated by TRH. Similarly, there was no TSH increase after 5 out of 33 TRH tests of normal dogs and 7 of 70 tests in apparently euthyroid patients, in spite of normal T-4 and prolactin responses. Furthermore, 4 hypothyroid dogs had norm al TSH and 6 euthyroid dogs had elevated TSH-levels. We conclude that the new TSH assay systems are valuable tools for the investigation of thyroid physiology and illness in the dog. With our current knowledge we recommend that the TRH-stimulation test is still necessary for the diagnosis of canine hypothyroidism.