Risk Factors for Permanent Hypocalcemia after Total Thyroidectomy in Patients with Papillary Thyroid Carcinoma

Total thyroidectomy remains the primary treatment for patients with papillary thyroid carcinoma but carries a risk of permanent hypocalcemia. This cohort study aimed to identify indicators of permanent hypocalcemia, including optimal testing times and diagnostic thresholds. Patients with papillary thyroid carcinoma who underwent total thyroidectomy at our institution between August 2021 and March 2023 were retrospectively enrolled. Serum parathyroid hormone, calcium, magnesium, and phosphorus levels and other potential predictors were assessed preoperatively and 1 day and 1, 3, and 6 months postoperatively. Ninety-two patients were included. Independent samples t-tests revealed significant correlations of permanent hypocalcemia with the parathyroid hormone level on postoperative day 1 (P = 0.031) and its percentage decline (ΔPTH) (P = 0.002). Only ΔPTH was a consistently significant risk factor for permanent hypocalcemia when patients were stratified by sex (P = 0.014 for men, P = 0.013 for women) and age (P = 0.006 for < 50 years, P = 0.040 for ≥ 50 years). The area under the receiver-operating characteristic curve was 0.65 (95% CI 0.53–0.77) for parathyroid hormone on postoperative day 1 with an optimal diagnostic threshold of 5.2 pg/mL and 0.69 (95% CI 0.57–0.80) for ΔPTH with an optimal cut-off of 62.5%. Restricted cubic spline analysis showed a linear relationship between ΔPTH and permanent hypocalcemia (P = 0.17). The parathyroid hormone level on postoperative day 1 and ΔPTH can predict the risk of permanent hypocalcemia after total thyroidectomy for papillary thyroid carcinoma. However, ΔPTH is a better predictor than the parathyroid hormone level on postoperative day 1 and has a diagnostic threshold of 62.5%.