Intraoperative PTH monitoring during parathyroid surgery: when 10 minutes is not enough-Can delayed decline be...

A substantial proportion of patients undergoing focused parathyroidectomy fail to meet the "≥50% intraoperative parathyroid hormone (ioPTH) drop" criterion at 10 min despite ultimately achieving biochemical cure. This study aimed to determine the frequency of delayed ioPTH decline and associated factors.

We conducted a retrospective cohort study including patients with primary hyperparathyroidism undergoing successful parathyroidectomy for uniglandular disease with ioPTH monitoring between 2017 and 2023. Blood samples were obtained at baseline, 5, 10, and 15-20 min after gland excision. Additional measurements beyond 20 min were collected at the surgeon's discretion. Delayed responders (DR) were defined as patients achieving a ≥ 50% ioPTH decrease from the pre-incision baseline later than 10 min. Univariable analyses and multivariable Firth-penalized logistic regression identified predictors of delayed response.

A total of 190 patients were included. A ≥ 50% ioPTH decline was achieved at 10 min in 160/190 patients (84.2%), whereas 30/190 (15.8%) were classified as DR. Of these, 22/190 (11.6%) met the criterion at 15-20 min and 8/190 (4.2%) beyond 20 min. Half of DR exhibited a 10-min ioPTH decline within the 40.0%-49.9% range. A manipulation-induced 5-min ioPTH spike occurred exclusively among DR (44.8% vs 0%; p < 0.001). Baseline ioPTH <100 pg/mL (10.6 pmol/L) was also strongly associated with delayed biochemical decline (50.0% vs 12.2%; p = 0.0003). Both factors remained significant in multivariable analysis.

One in six patients undergoing successful parathyroidectomy exhibited a delayed biochemical response. Low baseline ioPTH levels and manipulation-induced PTH spikes were strong independent predictors. Careful interpretation of early ioPTH kinetics and delayed sampling, particularly after a substantial but insufficient 10-min decline, may reduce unnecessary bilateral neck exploration in selected patients.