Measurement of serum total thyroxine, triiodothyronine, free thyroxine, and thyrotropin concentrations for diagnosis of hypothyroidism in dogs.

摘要

Baseline serum concentrations of total thyroxine (T4), triiodothyronine (T3), free T4, and thyroid-stimulating hormone (TSH) were measured in 54 dogs with confirmed hypothyroidism and 54 euthyroid dogs with non-thyroidal disease initially suspectedto have hypothyroidism. Reference ranges for hormone concentrations were established on the basis of results for 150 healthy dogs. Of the 54 hypothyroid dogs, 48 (89%) had low total T4 concentrations, whereas only 10 (18%) euthyroid dogs had low concentrations. Less than 10% of dogs in the hypothyroid and euthyroid groups had low T3 concentrations. Of the hypothyroid dogs, 53 (98%) had low free T4 concentrations. Only 4 (7%) euthyroid dogs had low free T4 concentrations. Of the hypothyroid dogs, 41 (76%) had high TSH concentrations whereas only 4 (7%) euthyroid dogs had high concentrations. It is concluded that serum total and free T4 and TSH determinations are useful tests for diagnosis of hypothyroidism in dogs. About a quarter of the dogs with confirmed hypothyroidism, however, will have serum TSH concentrations that remain within reference limits.