Changes of Circulating Thyroxine, Triiodothyronine and Reverse Triiodothyronine After Radiographic Contrast Agents

Abstract

Thyroid function was studied for 42 days in 58 patients, 28 of whom had euthyroid goiter, after urography (diatrizoic acid), cholangiography (ioglycamic acid), and cholecystography (Naiopanoate). After urography and cholangiography shortlived increases of the serum thyroxine occurred in a few patients, but the mean thyroxine and triiodothyronine concentration did not change. By contrast, 7 days after oral cholecystography serum thyroxine had risen consistently by 22% with a concomittant rise of the free thyroxine, while triiodothyronine declined by 15%. The thyroxine metabolite 3,3′,5′-triiodo-l-thyronine (reverse T₃) rose by 50% and serum thyrotropin concentration doubled. After 42 days thryoxine and triiodothyronine had returned to baseline, and none of the 58 patients developed clinical hyperthyroidism. In patients with severe myxoedema kept on a constant replacement dose with 1-thyroxine Na-iopanoate produced similar changes with the exception of the rise of the serum thyroxine. The primary event after Na-iopanoate seems to be a fall of the serum triiodothyronine, which in turn augments thyrotropin and indirectly thyroxine secretion. The marked and sometimes sustained rise of serum thyroxine after cholecystography may lead to the erroneous diagnosis of hyperthyroidism.