usefulness of iodinecreatinine ratio from spoturine samples to evaluate the effectiveness of lowiodine diet preparation for radioiodine therapy objective the success of a lowiodine diet lid is best determined by measurement of 24h urine iodine ui excretion the aim of this study was to determine reliable estimates for 24h ui based on spoturine samples and to provide cutoffs to determine the effectiveness of lid preparationdesign we prospectively measured iodine levels in 193 patients based on 24h and spoturine samples before radioactive iodine therapy the iodine was expressed as the 24h ui excretion microgday and as two different indices from spot urine simple iodine concentration simple i and the iodinecreatinine icr ratio poor lid preparation was defined as i excretion of 150 microgday according to the 24h ui measurementresults the measured 24h ui was significantly higher than the two indices from spot urine p 662 microgg cr sensitivity 964 specificity 836 positive predictive value 500 and negative predictive value 993conclusions we demonstrated that the icr ratio from spot urine could serve as a useful and reliable alternative to 24h urine collection as it has acceptable diagnostic values for detecting poor lid preparation