Low serum triiodothyronine and reverse triiodothyronine concentrations in patients with prolonged coma

We studied 10 patients (7 men and 3 women) hospitalized for prolonged coma (range, 61 to 1,320 days). The mean serum TBG and TSH concentrations were within the normal range for adults. However, the mean T ₃ concentration was significantly lower than normal. The mean rT ₃ concentration was not significantly different from normal. After TRF administration, there was a significant rise in mean serum TSH concentration, from 5.2 ± 0.6 to 11.3 ± 1.3 μunits/ml at 30 min. The rises in mean serum T ₄ and rT ₃ concentrations (to 10.6 ± 1.5 μg/dl and 22 ± 6 ng/dl, respectively) were not significant. However, there was a significant rise in mean serum T ₃ concentration, from 81 ± 13 to 146 ± 18 ng/dl 120 min after TRF injection.