C T Mooney1, C J Little, A W Macrae. 1. Department of Veterinary Medicine, University of Glasgow Veterinary School, Bearsden, Scotland.
Abstract
OBJECTIVE: To determine circulating concentrations and fate of total and free thyroxine (T4) in cats with various illnesses not associated with the thyroid glands (nonthyroidal illnesses). DESIGN: Prospective study. ANIMALS: 98 cats with nonthyroidal illness and 50 clinically normal cats. PROCEDURE: Serum total T4 concentrations were measured by radioimmunoassay, and serum free T4 concentrations were measured by direct equilibrium dialysis. Free T4 fraction was calculated from these 2 values. RESULTS: Serum total T4 concentrations were significantly (P < 0.001) lower in sick cats (mean +/- SD, 17.18 +/- 8.14 nmol/L), compared with healthy cats (mean +/- SD, 26.00 +/- 7.62 nmol/L). Serum total T4 concentrations were inversely correlated with mortality. Differences in serum free T4 concentrations in sick cats (mean +/- SD, 27.70 +/- 13.53 pmol/L), compared with healthy cats (mean +/- SD, 24.79 +/- 8.33 pmol/L), were not significant. A few sick cats had serum free T4 concentrations greater than the reference range. Calculated free T4 fraction was significantly (P < 0.001) greater in sick cats (mean +/- SD, 0.24 +/- 0.30%), compared with healthy cats (mean +/- SD, 0.10 +/- 0.06%). CLINICAL IMPLICATIONS: Euthyroidism is maintained in sick cats, despite low serum total T4 concentrations. Measurement of serum total T4 concentrations is a valuable prognostic indicator. Serum free T4 concentrations should be used cautiously as a sole diagnostic criterion for confirmation of hyperthyroidism.
OBJECTIVE: To determine circulating concentrations and fate of total and free thyroxine (T4) in cats with various illnesses not associated with the thyroid glands (nonthyroidal illnesses). DESIGN: Prospective study. ANIMALS: 98 cats with nonthyroidal illness and 50 clinically normal cats. PROCEDURE: Serum total T4 concentrations were measured by radioimmunoassay, and serum free T4 concentrations were measured by direct equilibrium dialysis. Free T4 fraction was calculated from these 2 values. RESULTS: Serum total T4 concentrations were significantly (P < 0.001) lower in sick cats (mean +/- SD, 17.18 +/- 8.14 nmol/L), compared with healthy cats (mean +/- SD, 26.00 +/- 7.62 nmol/L). Serum total T4 concentrations were inversely correlated with mortality. Differences in serum free T4 concentrations in sick cats (mean +/- SD, 27.70 +/- 13.53 pmol/L), compared with healthy cats (mean +/- SD, 24.79 +/- 8.33 pmol/L), were not significant. A few sick cats had serum free T4 concentrations greater than the reference range. Calculated free T4 fraction was significantly (P < 0.001) greater in sick cats (mean +/- SD, 0.24 +/- 0.30%), compared with healthy cats (mean +/- SD, 0.10 +/- 0.06%). CLINICAL IMPLICATIONS: Euthyroidism is maintained in sick cats, despite low serum total T4 concentrations. Measurement of serum total T4 concentrations is a valuable prognostic indicator. Serum free T4 concentrations should be used cautiously as a sole diagnostic criterion for confirmation of hyperthyroidism.
Authors: M Galgano; I Spalla; C Callegari; M Patruno; E Auriemma; G Zanna; S Ferro; E Zini Journal: J Vet Intern Med Date: 2014-01-13 Impact factor: 3.333
Authors: Mark E Peterson; Danielle L Davignon; Nicole Shaw; Eric Dougherty; Mark Rishniw; John F Randolph Journal: J Vet Intern Med Date: 2020-10-01 Impact factor: 3.333