LONGITUDINAL-STUDY OF IODINE IN TOENAILS FOLLOWING IV ADMINISTRATION OF AN IODINE-CONTAINING CONTRAST AGENT

The literature on the relationship between diet and thyroid cancer (TC ) risk and the higher incidence of TC among Asian immigrants to the US compared to second and third generation subgroups has prompted epidem iologists to hypothesize that increased levels of iodine consumption m ay be associated with TC risk, particularly among persons with a histo ry of clinical or subclinical thyroid dysfunction. At the University o f Missouri Research Reactor (MURR), we have applied epiboron neutron a ctivation analysis to investigate human nails as a dietary monitor for iodine. Preliminary studies have indicated a positive correlation bet ween dietary iodine intake and the concentration of iodine in toenails . However, these studies are confounded by high iodine levels (up to 3 0 ppm) in approximately 5% of the nails studied. We hypothesize that, in the subjects we have studied, the high iodine levels may be due to iodine-containing medications, in particular contrast-agents containin g iopamidol. This paper will report on longitudinal studies using cont rast agent subjects who were followed-up for almost two years compared to a longitudinal control and a population mean. Based on this study, we suggest that iodine-containing contrast agents contaminate nail sa mples via non-specific binding in the short term followed by incorpora tion in the nail as a result of absorption.