Prediction of Transient and Permanent Hypoparathyroidism after Total Thyroidectomy Using the Postoperative Serum Parathyroid Hormone Test: When Is the Best Time to Check?

Abstract

Purpose The usefulness of serum intact parathyroid hormone (iPTH) levels for predicting hypocalcemia after total thyroidectomy is well established. This retrospective cohort study aimed to identify the best time iPTH levels should be checked, and determine the postoperative day 1 iPTH level that most safely predict the development of permanent hypoparathyroidism after total thyroidectomy. Methods All consecutive patients who underwent total thyroidectomy in 2013–2015 were identified, retrospectively. iPTH was measured at 2 hours after thyroidectomy, and on postoperative days 1 and 2, and 12 months after surgery. Results In total, 730 patients were included. Their iPTH levels on postoperative day 2 correlated better with postoperative day 1 levels (Pearson's r=0.915) than with iPTH levels at 2 hours after total thyroidectomy (r=0.786). Fourteen patients had normal iPTH levels at 2 hours after thyroidectomy but abnormal levels on postoperative days 1 and 2. On the other hand, 38 patients had abnormal iPTH levels at 2 hours after thyroidectomy but normal values on postoperative days 1 and 2. Receiver operating characteristic analysis showed that the iPTH value of 3.05 pg/mL best predicted permanent hypoparathyroidism (sensitivity, 92.9%; specificity, 99.7%). The safe cutoff value was 9.65 pg/mL (sensitivity, 70.9%; specificity, 100%). Conclusion A single measurement of iPTH on postoperative day 1 predicted patients at risk of transient hypocalcemia more accurately than measurements at 2 hours after surgery, and thus, can serve widely as a predictor of permanent hypoparathyroidism.