What is the most appropriate intraoperative baseline parathormone? A prospective cohort study.

Introduction: The time of drawing pre-incision intraoperative parathyroid hormone (ioPTH) is crucial to provide the right baseline for post-excision PTH measurement. The objective of this study was to identify the optimal time and the numbers of baseline PTH samples that best predict excision of all hypercellular parathyroid tissue when compared with 10-min post-excision PTH level.

Materials And Methods: In this prospective study, two pre-incision (pre-induction and 10-min post-induction) baseline ioPTH samples along with pre- and post-excision ioPTH were collected and analyzed for 352 parathyroidectomies in 341 patients for sporadic primary hyperparathyroidism at a University hospital. Paired Wilcoxan signed rank test was used to compare the pre-incision ioPTH levels and their percent drop to 10-min post-excision levels. Sensitivity, specificity, predictive values and receiver operating characteristic (ROC) curves were used to compare the predictability of the two pre-incision levels.

Results: The difference between pre- and post-induction baseline PTH levels was highly significant (p < 0.001). In 4% cases the criterion of post-excision PTH drop of ≥50% was achieved only with the post-induction baseline PTH and not with pre-induction PTH measurement. Using pre-induction baseline, ioPTH had an overall accuracy of 90% whereas ≥50% fall in the post-excision PTH from the post-induction baseline PTH had the accuracy of 94.85%.

Discussion: There was a significant difference between pre- and post-induction PTH levels and Miami criteria was met in 95.45% cases with post-induction baseline.

Conclusions: The optimal time for drawing pre-incision baseline PTH sample is at 10 min post-induction of general anesthesia and positioning of patient.