Thyroid function in critically ill infants with infections.

To investigate thyroid function in critical illness in infancy, serum thyroxine (T4), triiodothyronine (T3), reverse triiodothyronine (rT3) and thyroid-stimulating hormone (TSH) concentrations were measured in serum in 13 such patients. T4 and TSH values were found to be comparable to control values, while T3 values were significantly low and rT3 values were high. When the patients were evaluated according to prognosis, significantly lower initial and subsequent T4 values were found in the fatal group as compared with the control group. Initial T3 concentrations both in fatal cases and in patients who recovered were significantly lower than those in the controls. Subsequent T3 values in the group who recovered showed a relative increase, but in the fatal cases a further decrease, in T3 levels, accompanied by a decrease in rT3 levels to values comparable to those of the controls, was observed in the terminal stage.