Free T4, Free T3, and Reverse T3 in Critically III, Thermally Injured Patients

Abstract

A prospective study of thyroid function was performed in 25 thermally injured patients. These patients are divided into 2 groups. The 1st group contains 5 patients with greater than 50% burn size studied longitudinally during the first 15 days following thermal injury. Significant suppression of serum concentrations of 3,5,3''-triiodothyronine (T3) and elevation of serum concentrations of 3,3'',5''-triiodothyronine (rT3) were seen. The free thyroxine [T4] index and serum thyrotropin concentrations remained within the normal range. To assess the clinical significance of these alterations in peripheral thyroid hormone concentrations, a 2nd group of 20 patients was studied. The free serum levels of T4 (FT4) and T3 (FT3) were measured in 10 patients, mean age 34 yr, mean burn size 56%, studied during a period of clinical deterioration, and in 10 patients of comparable age and burn size who were clinically stable. Both FT4 and T3 values were significantly lower in the unstable patients (P < 0.01). All FT3 values for the unstable patients (mean .+-. SE), 193 .+-. 14 pg/dl, were below the normal range for FT3 of 230-669 pg/dl, and significantly lower than those observed in the stable patients (mean .+-. SE), 430 .+-. 59 pg/dl (P < 0.001). This correlation of biochemical hypothyroidism with clinical deterioration may have functional significance for the critically ill trauma patient.