Intraoperative parathyroid hormone levels in thyroid and parathyroid surgery

OBJECTIVE: To determine the utility of intraoperative parathyroid hormone measurement in predicting postoperative hypocalcemia after thyroid and parathyroid surgeries that places total parathyroid function at risk. STUDY DESIGN: Retrospective case review. METHODS: The case records of 23 patients undergoing total or completion thyroidectomy and 30 patients undergoing parathyroid exploration were reviewed. All patients had intraoperative parathyroid hormone levels measured. Samples were taken before dissection and 10 minutes after the resection was completed. Serial ionized calcium levels were measured in the postoperative period. Percentages of reduction in PTH levels from preoperative to postresection levels were calculated. Percentages of reduction in PTH level and the absolute value of the intraoperative PTH values were compared with postoperative ionized calcium levels. RESULTS: In the 23 patients who underwent thyroid surgery, the average preoperative and postoperative PTH values were 50 pg/mL (range, 17-87 pg/mL) and 34 pg/mL (range, 4-93 pg/mL), respectively. The average decrease in PTH was 39% (range, 39%-90%). The incidence of hypocalcemia was significantly higher in patients with intraoperative PTH levels less than 15 pg/mL relative to patients with PTH levels greater than 15 pg/mL in this setting ( P=.006). In the 30 patients who underwent parathyroid exploration, average preoperative and postoperative PTH levels were 291 pg/mL (range, 65-1675 pg/mL) and 113.8 pg/mL (range, 6.5-1263 pg/mL) respectively. The intraoperative PTH level did not correlate with postoperative calcium levels in the parathyroid group. Percentages of decrease in PTH levels greater than 60% was statistically associated with surgical cure in this population. CONCLUSIONS: The study demonstrates that intraoperative PTH levels greater than 15 pg/mL after total or completion thyroidectomy indicate a low risk of postoperative hypocalcemia and that these patients may be candidates for outpatient surgery. In the parathyroid group, intraoperative PTH levels do not correlate well with postoperative calcium levels.