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

This study investigated 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 azotaemia after 131I treatment (group 3). Serum TT4 responses and thyroidal pertechnetate uptake after administration of 25 μg rhTSH IV were assessed. Baseline serum TT4 was significantly lower in group 3 compared with group 1, but not between other group pairs. 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. Thyroid/salivary gland uptake ratio (T/S uptake ratio) differed only significantly between groups 1 and 3. Stimulation with rhTSH is valuable to differentiate euthyroidism from iatrogenic hypothyroidism in cats.