The final intraoperative parathyroid hormone level: how low should it go?

BACKGROUND: In minimally invasive surgery for primary hyperparathyroidism (HPT), intraoperative parathyroid hormone (IOPTH) monitoring assists in obtaining demonstrably better outcomes, but optimal criteria are controversial.

METHODS: The outcomes of 1,108 initial parathyroid operations for sporadic HPT using IOPTH monitoring from 1997 to 2011 were stratified by final post-resection IOPTH level. All patients had adequate follow-up to verify cure.

RESULTS: With mean follow-up of 1.8 years (range 0.5-14.3 years), parathyroidectomy using IOPTH monitoring failed in 1.2 % of cases, with an additional 0.5 % incidence of long-term recurrence at a mean of 3.2 years (range 0.8-6.8 years) postoperatively. Operative success was equally likely with a final IOPTH drop to 41-65 pg/mL vs ≤40 pg/mL (p = 1). In the 76 patients with an elevated baseline IOPTH level that did not drop to ≤65 pg/mL, surgical failure was 43 times more likely than with a drop into normal range (13 vs. 0.3 %; p < 0.001). When the final IOPTH level dropped by >50 % but not into the normal range, surgical failure was 19 times more likely (3.8 vs. 0.2 %; p = 0.015). Long-term recurrence was more likely in patients with a final IOPTH level of 41-65 pg/mL than with a level ≤40 pg/mL (1.2 vs. 0; p = 0.016).

CONCLUSIONS: Adjunctive intraoperative PTH monitoring facilitates a high cure rate for initial surgery of sporadic primary hyperparathyroidism. A final IOPTH level that is within the normal range and drops by >50 % from baseline is a strong predictor of operative success. Patients with a final IOPTH level between 41-65 pg/mL should be followed beyond 6 months for long-term recurrence.