Background: Since approximately 10% of hyperthyroid cats have a normal TT4, TSH may be needed to confirm the diagnosis. Until recently, only a canine TSH assay (cTSH) was available, which cannot differentiate between subnormal and low-normal TSH concentrations in cats. A novel feline-optimized TSH assay (fTSH, Truforma Zomedica) differentiates better between euthyroid and hyperthyroid cats, but the effect of non-thyroidal illness (NTI) is unknown.
Hypothesis: We aim to compare fTSH and cTSH concentrations among hyperthyroid, NTI, and healthy cats, and to evaluate the sensitivity and specificity of fTSH to diagnose hyperthyroidism.
Animals: The study enrolled 102 client-owned cats, including 37 hyperthyroid, 33 healthy, and 32 NTI cats.
Methods: Prospective cross-sectional study. TT4, cTSH and fTSH were measured in all cats. Hyperthyroidism was confirmed with thyroid scintigraphy. TSH was compared among groups using Kruskal Wallis followed by Wilcoxon pairwise method. Significance set at P<0.05.
Results: The sensitivity and specificity of fTSH are 78% (95% CI 62-90%) and 97% (84-100%), respectively. There is a significant difference between hyperthyroid cats and healthy and NTI cats with both assays (P <0.01).
Conclusion: The fTSH is useful to diagnose feline hyperthyroidism because it has a high specificity, identifies normal TSH in healthy cats more often, and appears to not be affected by NTI.
