The Role of Endogenous Cortisol in Patients with Non‐Thyroidal Illness and Decreased T3 Levels

The aim of the study was to elucidate if endogenous cortisol, as previously suggested, could be involved in the mechanism behind the reduced serum T3 levels seen in euthyroid patients with various non-thyroidal illnesses. The correlation between the serum levels of T3 and cortisol was investigated in 41 hospitalized patients with non-thyroidal illness during hyperpyrexia. The results showed a correlation coefficient of -0.94, indicating a close reciprocal association between the two hormones. Cortisol may thus be one factor associated with the decreased T3 levels seen in euthyroid patients with non-thyroidal illness. The results also indicate a close parallelism between the total and free T3 levels during hyperpyrexia.