The Final Intraoperative Parathyroid Hormone Level: How Low Should It Go?

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

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.

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).

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.