Prognostic significance of high free T4 and low free T3 levels in non-thyroidal illness syndrome

Abstract

BackgroundNon-thyroidal illness syndrome is characterized by decreased serum free T3 (FT3) level and associates with long term mortality. Serum free T4 (FT4) may affect on mortality with FT3 in course of chronic illness. This study performed to evaluate the association between both decreased FT3 with elevated FT4 levels and mortality risk. MethodsThis study is a retrospective cohort analysis and consisted up 1164 (571 male, 593 female) patients with a 36 months follow up period. Patients divided into four groups according to thyroid functions. Patients with euthyroidism were in Group A, elevated FT3 in group B, decreased FT3 in group C and both decreased FT3 and elevated FT4 levels in group D. The levels of thyroid hormones and all cause mortality were compared between four groups. ResultsMortality rate was elevated between Groups A and B, A and C, A and D, B and C, B and D, C and D, (p < .001, p < .001, p < .001, p < .001, p < .001, p:0.019, respectively). A multivariate Cox proportional hazards model was performed to evaluate the mortality risk between groups. A close relationship was observed in Group C and D patients for the mortality risk (OR:1.561, 95% CI:1.165–2.090, p:0.003 and OR:2.224, 95% CI:1.645–3.006, p:0.0001, respectively). ConclusionBoth decreased FT3 and elevated FT4 levels are independent predictor for long term mortality risk in hospitalized chronic patients with non-thyroidal illness syndrome.