EFFECTS OF AN ORGANIC IODINE COMPOUND (PRIODAX) ON TESTS OF THYROID FUNCTION*

Abstract

VARIOUS organic iodine compounds used in radiology affect the succeeding tests of thyroid function. Certain iodine-containing compounds become associated with proteins in the serum (1) and are measured as protein-bound iodine. The serum protein-bound iodine (PBI), considered normally to consist predominantly of thyroxine, is therefore artefactually elevated. Some of the organic iodine compound does not associate with protein and the total iodine is raised, therefore, by an elevation in PBI, unbound organic iodine compound and iodide. The uptake by the thyroid of radioactive iodine may be reduced below normal. It has been assumed that this is due to a release from the organic iodine molecule of inorganic iodide—sometimes slowly over a long period of time. The development of myxedema following administration of organic iodine has been reported (2). The comparison of total iodine with PBI often indicates contamination with inorganic iodide or with organic iodine compounds un associated with protein. Butanol does not extract the protein-iodine complex which is formed when iodide levels have been high for some time, and serves to differentiate this artefactual elevation of PBI. Certain organic iodine compounds associated with protein, however, are soluble in butanol and thus both the PBI and BEI levels will be misleadingly elevated (3).