Hyperthyroidism in cats: should we be routinely testing for early diagnosis?

Abstract

Background: Routine testing for hyperthyroidism could become standard practice in all cats, before the onset of clinical signs. Aims: To describe serum total thyroxine (T4) concentration levels in a population of clinically normal cats; to determine the range of T4 levels in clinically normal cats; to estimate the prevalence of hyperthyroidism in clinically normal cats and to identify risk factors for elevated T4 levels in clinically normal cats tested for hyperthyroidism and are diagnosed. Methods: Total T4 records of 202 clinically normal cats, tested for routine pre-anaesthetic bloods, using a Quantum Saturno 100 Vet wet chemistry analyser, were analysed retrospectively. Any result above or below the normal reference range was classified as being hypo/hyperthyroid. Statistical Package for Social Sciences (SPSS) software assisted in the analysis of blood results and highlighted risk factors associated with the disease. Results: Out of the 202 clinically normal cats, 76 did, in fact, have hyperthyroidism. There was a statistically significant association between breed and T4 result, with a much higher prevalence of hyperthyroidism and higher median T4 result in purebreed cats compared with crossbreed cats. Thus providing evidence that routine testing on all purebreed cats could be worthwhile. Age, weight, gender, neutered status and colour were not significantly associated with hyperthyroidism or T4 result. Conclusion: Purebreed cats are a group that could be routinely tested for hyperthyroidism, as results showed a statistically significant association between breed and T4 result.