A Low Incidence of Iodine-Induced Hyperthyroidism Following Administration of Iodinated Contrast in an Iodine-Deficient Region.

ObjectiveThere are limited data on the incidence of iodinated contrast-induced thyrotoxicosis, particularly in iodine-deficient regions. The aim of this study was to determine the incidence of iodinated contrast-induced thyrotoxicosis and to determine whether thyrotoxicosis was more common in patients 70years compared to those <70years of age.DesignA prospective study of adult patients undergoing an outpatient CT with iodinated contrast was performed.MeasurementsThyroid function tests (TFTs) and urine iodine measurements were performed prior to the scan. TFTs were repeated at 4- and 8-weeks postscan. Changes in TFTs from baseline were analysed.ResultsA total of 102 patients were included in the final analysis. Overall, TSH levels dropped (P=00002), and free T-3 (FT3) levels increased (P=004) between baseline and week 4 with normalization by week 8; however, these changes were not considered clinically significant. No significant differences in free T-4 (FT4) occurred in the overall group (P=082). There were no differences in TFTs between baseline and 4 or 8weeks for those patients aged <70 compared to 70years. Two patients developed new subnormal TSH values. Of these, one had a 90-mm follicular variant papillary thyroid carcinoma diagnosed while the other had a normal thyroid assessment and TSH spontaneously normalized by 12weeks.ConclusionsOnly 2% of patients developed subclinical hyperthyroidism following a standard dose of iodinated contrast for CT investigations. Given the low incidence of iodine-induced thyrotoxicosis, there is no indication for routine pre- and post-CT thyroid function testing in our region.