Thyroid uptake and imaging with iodine-123 at 4-5 hours: replacement of the 24-hour iodine-131 standard.

A study was carried out to determine the suitability of utilizing a 4 to 5 hr interval from administration of iodine-123 to imaging and uptake measurement as a replacement for the 24-hr standard originally established with iodine-131. In 55 patients who underwent scintigraphy at 4 and 24 hr, there was no discrepancy between paired images. In 55 patients who had uptake measured at 4 and 24 hr and in 191 patients who had uptake measured at 5 and 24 hr, the early measurements proved equal or better discriminants of euthyroid from hyperthyroid patients. In our institutions, these findings and the logistical advantages of completing the exam in 4-5 hr led us to abandon the 24-hr study in the majority of patients.