Serum thyroxine and thyrotropin concentrations decrease with severity of nonthyroidal illness in cats and predict 30-day survival outcome

Abstract

Background: In cats, nonthyroidal illness affects serum thyroid hormone concentrations. Serum thyroxine (T4) and triiodothyronine (T3) concentrations commonly decrease, whereas free T4 (fT4) concentrations vary unpredictably. Limited information exists regarding effects on serum thyrotropin (thyroid-stimulating hormone [TSH]) concentrations in cats with nonthyroidal illness syndrome (NTIS). Objectives: To characterize alterations in thyroid function that develop in cats with NTIS and to correlate these alterations with severity and outcome of the nonthyroidal illness. Animals: Two hundred and twenty-two cats with NTIS and 380 clinically normal cats of similar age and sex. Methods: Prospective, cross-sectional study. All cats had serum T4, T3, free T4, and TSH concentrations measured. Cats were grouped based on illness severity and 30-day survival. Results: Cats with NTIS had lower serum T4 and T3 concentrations than did normal cats (P