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Thyroid Testing in Cats

van Hoek IM, Vandermeulen E, Peremans K et al: Thyroid stimulation with recombinant human thyrotropin in healthy cats, cats with non-thyroidal illness and in cats with low serum thyroxin and azotaemia after treatment of hyperthyroidism, J Feline Med Surg 12:117, 2010.

Investigators studied the recombinant human thyrotropin (rhTSH) stimulation test in healthy cats (Group 1), cats with non-thyroidal illness (Group 2) and cats with low serum total T4 (TT4) and azotemia after I-131 treatment (Group 3). Radioiodine (131)is the treatment of choice for hyperthyroidism, yet iatrogenic hypothyroidism can occur in 6-30% of cases post-treatment. Complicating this, up to 39% of treated cats have chronic kidney disease (CKD). When a low circulating serum TT4 concentration is found in cats treated with I-131, non-thyroidal illness (NTI) has to be considered, especially CKD, before a diagnosis of iatrogenic hypothyroidism can be confirmed. With the consideration that hypothyroidism can decrease renal function, a diagnosis of hypothyroidism or NTI is necessary. Serum TT4 increased significantly in groups 1 and 2, but not in group 3 after rhTSH administration. Post-rhTSH serum TT4 concentrations differed significantly between groups 1 and 3 and groups 2 and 3, but not between groups 1 and 2. Based on the marginal increase in serum TT4 concentration, compared to the healthy cats and cats with NTI, the conclusion was that all four cats from Group 3 had iatrogenic hypothyroidism. The study results suggest a TT4 measurement before and after rhTSH is a clinically useful test and can reliably evaluate thyroid function and differentiate euthyroidism from iatrogenic hypothyroidism in cats. [VT]

Related articles:
van Hoek IM, Peremans K, Vandermeulen E et al: Effect of recombinant human thyroid stimulating hormone on serum thyroxin and thyroid scintigraphy in euthyroid cats, Journal of Feline Medicine & Surgery 11:309, 2009.