Decreased serum triiodothyronine is associated with increased concentrations of tumor necrosis factor

Previous studies in laboratory animals have shown that tumor necrosis factor-alpha (TNF) may alter thyroid function tests. To determine whether elevated serum TNF levels are associated with altered serum concentrations of T4, T3, free T4, rT3, and TSH, we measured these parameters in 29 nursing home residents with detectable serum TNF levels and compared the levels to those found in 36 patients with undetectable serum TNF levels. The 2 groups were matched for age, sex, clinical problems, use of medications, and nutritional status. Patients with detectable serum TNF levels had significantly lower serum T3 concentrations compared to those with undetectable levels [1.072 +/- 0.588 vs. 1.621 +/- 0.594 nmol/L (mean +/- SD); P less than 0.01]. Differences in other tests did not achieve statistical significance. Thyroid function tests were not significantly different when patients with detectable interleukin-1 alpha levels, another cytokine secreted during endotoxemia, were compared to those with undetectable levels. These observations taken together with the previous findings in laboratory animals suggest that some of the alterations in thyroid hormone levels seen in nonthyroidal illness are associated with elevated serum concentrations of TNF.