Free thyroxine concentrations in thyroid storm.

Total serum thyroxine concentrations, the dialyzable fractions of total thyroxine, and absolute free thyroxine concentrations were measured in six patients with thyroid storm, in 15 patients with uncomplicated thyrotoxicosis, and in 19 normal subjects. Total thyroxine concentrations were similar in both thyrotoxic groups. However, the mean dialyzable fraction of thyroxine and the mean free thyroxine concentration was significantly higher in patients with thyroid storm than in patients with uncomplicated thyrotoxicosis (0.060 +/- 0.017% versus 0.026 +/- 0.006% and 10.9 +/- 3.8 ng/dL versus 4.7 +/- 1.4 ng/dL, respectively). These findings suggest that events precipitating thyroid storm may act with thyrotoxicosis to decrease thyroxine binding markedly and result in a sharp increase in free thyroxine concentration. These phenomena may play a role in the pathogenesis of thyroid storm.