Transient hyperthyroxinemia in symptomatic hyponatremic patients.

Twenty-two patients with severe hyponatremia were divided into 12 patients with and ten without associated neurologic manifestations (groups 1 and 2, respectively). Marked hyperthyroxinemia was demonstrated in seven patients in group 1 but in none in group 2. The triiodothyronine concentration was also higher than normal in two patients in group 1. All serum iodothyronine concentrations in group 1 were significantly higher than in group 2. Thyrotropin and thyroxine-binding globulin levels were normal in both groups. The differences between groups were apparent only in the acute phase, and there were no clinical manifestations of hyperthyroidism. All iodothyronine concentrations returned to normal within two weeks after the correction of the hypo-osmolar disorder. Our results indicate that a transient asymptomatic increase in serum iodothyronine levels occurs during hyponatremia. Thus, thyroid test results should be interpreted cautiously in patients with acute, severe, symptomatic hyponatremia.