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OBJECTIVE: To determine if final intraoperative parathyroid hormone (IOPTH) level predicts those at risk for recurrence after parathyroidectomy. Minimally invasive parathyroid exploration guided by preoperative imaging and IOPTH level is an accepted alternative to bilateral exploration for the treatment of primary hyperparathyroidism (HPT). However, additional enlarged, hypercellular parathyroid glands are present in some patients in whom IOPTH levels fall to normal after excision of a single adenoma. At least 15% of patients are normocalcemic with elevated PTH levels (PPTH) after parathyroidectomy. In these patients, a higher risk of recurrent HPT has been found. DESIGN: Retrospective review of medical records. SETTING: University teaching hospital. PATIENTS: The records of all 194 patients who underwent successful initial parathyroidectomy for nonfamilial HPT in 2007 and 2008 by 1 surgeon were reviewed. MAIN OUTCOME MEASURES: Intraoperative PTH level was measured prior to incision (baseline); at excision of the abnormal gland; at 5, 10, 15, and 20 minutes after excision; and at various additional times as needed. Of the patients, 71% underwent minimally invasive parathyroid exploration. Calcium, PTH, and 25-hydroxyvitamin D levels were measured during the first month after surgery in all patients and after 3 months or more in 80%. Patients were divided into 5 groups depending on the following final IOPTH levels: lower than 10 pg/mL (group l) (to convert PTH to nanograms per liter, multiply by 1.0); 10 to 19 pg/mL (group 2); 20 to 29 pg/mL (group 3); 30 to 39 pg/mL (group 4); and 40 pg/mL or higher (group 5). RESULTS: Of the patients, 82% had a single adenoma, 9% had double adenomas, and 9% had 3 or more abnormal glands. The final IOPTH/baseline IOPTH value in groups 1 to 5 was 7%, 11%, 16%, 23%, and 26%, respectively. There was no significant difference in the preoperative calcium among the groups. All 3 patients with persistent HPT and 5 patients with PPTH were in group 5. One of the 96 patients in groups 1 and 2 and 5 of the 72 patients in groups 3 and 4 had PPTH at the last evaluation. CONCLUSION: Patients with a final IOPTH level of 40 pg/mL or higher are at higher risk of having persistent HPT and should be followed up closely and indefinitely following parathyroidectomy