The quick parathyroid hormone assay (QPTH) reliably measures intact parathyroid hormone (iPTH) levels intraoperatively. The accuracy in predicting postoperative calcemia is related to blood sample timing and the criteria applied. To improve specificity or to decrease the cost of QPTH, several criteria have been used to predict complete excision. This study compares the Miami criterion with other published QPTH criteria in predicting operative outcome. QPTH and the Miami criterion (iPTH drop > or =50% from the highest of either preincision or pre-excision level at 10 minutes after gland excision), were used to predict postoperative calcium levels of 341 consecutive patients with sporadic primary hyperparathyroidism who were followed > or =6 months after the operation or recognized as operative failures. Intraoperative iPTH values of these patients were reanalyzed with the use of 5 published criteria to predict complete resection. Postoperative calcium levels were correlated with criteria predictions. Miami criterion correctly predicted postoperative calcium levels in 329 of 341 patients and was incorrect in 12 (3 false positives, 9 false negatives). With the use of other criteria, 2 of the 3 false-positive results would be prevented, but the 3% rate of false-negative predictions would increase to between 6% and 24%, causing unnecessary neck explorations to search for multiglandular disease. Surgeons trying to increase QPTH specificity significantly decrease the accuracy and intraoperative usefulness of the assay. The Miami criterion has the highest accuracy when compared with other criteria.