Utility of intraoperative parathyroid hormone measurement in predicting postparathyroidectomy hypocalcemia

Objective: To evaluate the role of a standardized intraoperative parathyroid hormone (PTH) assay in predicting postoperative hypocalcemia following parathyroidectomy for primary hyperparathyroidism. Study Design: Prospective series of 66 patients undergoing unilateral or bilateral parathyroidectomy between January 2004 and June 2005. Setting: Tertiary care centre in Vancouver, British Columbia. Methods: Preoperatively, ionized calcium and PTH levels were recorded. A standardized intraoperative PTH assay was used to measure PTH levels on all patients at the following times: just prior to initial incision (Ti), just prior to adenoma excision (T0), and 5 and 10 minutes after excision (T5 and T10, respectively). Calcium levels were drawn at 8 and 16 hours postoperatively. Clinically significant hypocalcemia was defined as a symptomatic patient or a serum ionized calcium ≤ 1.1 mmol/L. Main Outcome Measures: Postoperative hypocalcemia following parathyroidectomy. Results: The incidence of postoperative hypocalcemia was 12% (8 of 66). There was no significant correlation between postoperative hypocalcemia and any of the evaluated factors, including intraoperative values of PTH (all p > .05). The percentage change between ioPTH at Ti and at T10 was, however, significantly associated with the development of postoperative hypocalcemia (odds ratio = 3.47 for a 10% decline, p = .03). Conclusions: Percentage change in intraoperative PTH levels between the initial incision and at 10 minutes post-parathyroid adenoma excision is a significant predictor of postoperative hypocalcemia following parathyroidectomy for primary hyperparathyroidism.