Cut-off points of parathyroid hormone and serum calcium for post-thyroidectomy hypocalcemia prediction and early management

Abstract

Postoperative parathyroid hormone (PTH) cut-off points with high sensitivity and specificity can predict post-thyroidectomy hypocalcemia (PTHC) early and accurately, leading to timely decisions regarding calcium supplementation. This retrospective chart review primarily aimed to determine the optimal cut-off point of PTH levels within the first 24 hours after total or completion thyroidectomy (PTH-24) for predicting PTHC, categorizing patients into low, intermediate, and high-risk groups. The secondary objective was to find the optimal cut-off point for calcium levels on postoperative day 1 (CCL-POD1) to predict PTHC in the intermediate-risk group. This study included inpatients at Chumphon Khet Udomsak Hospital from May 1, 2023, to April 30, 2025. The study included 86 eligible patients, with 43 (50.0%) developing PTHC. ROC analysis of PTH-24 levels to predict PTHC yielded an AUC of 0.943 (p<0.001). The optimal cut-off point is 9.04 pg/ml (with 93.02% sensitivity and 86.05% specificity). However, a cut-off value of 7.83 pg/ml yields a higher specificity of 95.35% and a positive predictive value of 94.70%. Meanwhile, a cut-off point of 19.35 pg/ml provides a higher sensitivity of 97.67% and a negative predictive value of 95.45%. In the intermediate-risk group PTH-24 between 7.84-19.35 pg/ml), ROC analysis of CCL-POD1 to predict PTHC resulted in an AUC of 1 (p<0.001). The optimal cut-off point was 8.18 mg/dl. In conclusion, patients with PTH-24 ≥19.36 pg/ml combined with CCL-POD1 ≥8.0 mg/dl, and those with PTH-24 between 7.84 - 19.35 pg/ml combined with CCL-POD1 ≥8.18 mg/dl, can safely be ruled out for postoperative hypocalcemia and discharged. Conversely, for PTH-24 ≤7.83 pg/ml, immediate initiation of calcium and calcitriol supplementation is recommended.