Bovine
thyrotropin (bTSH) stimulation testing has long been considered the gold standard for diagnosis of canine
hypothyroidism. Unfortunately, bTSH is no longer commercially available. Recently, the use of recombinant human
thyrotropin (
rhTSH) to perform
thyroid-stimulating hormone (TSH) stimulation testing in dogs was described. The cost of an
rhTSH vial (1.1 mg) limits the practical use of this product. The study reported here was performed to determine the effects of storing
rhTSH on the post-TSH increase of serum total (TT4) and free (FT4)
thyroxine concentrations during TSH stimulation testing in 12 euthyroid Beagles in a crossover trial. Three TSH tests with recombinant human
thyrotropin (
rhTSH; 91.5 microg IV) were performed on each dog during 3 different periods: 1 with freshly reconstituted
rhTSH (fresh); 1 with
rhTSH, reconstituted and stored at 4 degrees C for 4 weeks (refrigerated); and 1 with
rhTSH, reconstituted and frozen at -20 degrees C for 8 weeks (frozen). Blood samples for determination of TT4 and FT4 concentrations were collected before and 4 and 6 hours after
rhTSH administration. There was no significant difference in TT4 or FT4 concentration after stimulation with fresh, refrigerated, and frozen
rhTSH. Furthermore, there was no significant difference between TT4 or FT4 serum concentration observed 4 and 6 hours after
rhTSH administration. In conclusion, reconstituted
rhTSH can be stored at 4 degrees C for 4 weeks and at -20 degrees C for 8 weeks without loss of
biological activity, allowing clinicians to perform more TSH response tests per vial.