Evaluation of thyroid functions in critically ill infants.

The degree to which thyroid functions are affected by non-thyroid illness and an assessment of its correlation with mortality was evaluated. Thirty infants (20 M, 10 F) with a mean age of 433 +/- 3.28 months (+/- 1 SD), with severe acute systemic illness and 30 healthy controls, age and sex matched, were studied for total serum T3, T4 and TSH levels at admission and recovery or before death. Serum thyroid hormones were measured using standard techniques. There was no significant change in thyroid indices with age, sex, nutritional status, serum protein and C-reactive protein. Serum T3 levels in infants were significantly lower (0.62 +/- 0.63 ng/ml) than the controls (1.90 +/- 0.62) (p < 0.001), with normal T4 and TSH levels at admission. Both serum T3 and T4 levels increased with recovery. Out of 30 infants studied, 14 died whereas 16 were discharged. It was noticed that T3 and T4 values were significantly reduced at or near death when compared with the admission levels (p < 0.001). Prognosis could not be determined at the time of admission, as thyroid indices at admission of patients who died, when compared to infants who were discharged, showed no significant difference in T3, T4 or TSH levels. The above mentioned changes in thyroid indices probably occur as a temporary adaptive mechanism to limit catabolism in states of stress such as infection. Hence, it is suggested that thyroid function tests be interpreted with caution in patients with non-thyroid illness.