Thyroid function tests in domesticated animals: free thyroxine index
Kallfelz, F.A.; Erali, R.P.
American Journal of Veterinary Research 34(11): 1449-1451
1973
ISSN/ISBN: 0002-9645 PMID: 4748730 Document Number: 64399
Normal values for resin sponge uptake of labelled 3,5,3'-triiodothyronine (T-3) (T-3 test), total serum thyroxine (T-4) by competitive protein binding (T-4 test), and the free thyroxine index (FTI), a product of T-3 and T-4 test results (T-7 test), were determined as a function of age in 7 species of domesticated animals. Results indicate that serum T-4 concentration decreases significantly with age in dogs and in pigs, and T-3 uptake decreases with age in sheep and goats. In pigs, the T-3 values were highest in young adult animals. Serum T-4 concentrations seem lower in single-stomached animals than in ruminants, and there seems to be an inverse relationship between serum T-4 concentration and T-3 test results; species with higher serum T-4 concentrations had lower T-3 test results and species with lower serum T-4 concentrations had higher T-3 results. The results indicate that, at least in the dog, the T-3 test does not seem to be sensitive in detecting changes in thyroid status, and thus, the T-4 test alone could be as valuable as the FTI in this species.