**Abstract**

Severe hypocalcemia is a serious complication occurring after parathyroidectomy for secondary hyperparathyroidism. Totally, 322 patients who were successfully treated with total parathyroidectomy and bilateral thymectomy plus autotransplantation were studied. Group A (247 patients) developed mild hypocalcemia. Group B (75 patients) who had post-operative serum Ca levels <6.5 mg/dL or needed >4 g of intravenous (i.v.) Ca gluconate to keep Ca levels ≥6.5 mg/dL developed severe hypocalcemia. Preoperatively, patient age was recorded, and serum Ca, P, alkaline phosphatase (Alk-ptase), and intact parathyroid hormone (iPTH) levels were checked. These serum levels were checked again 18 h post-operatively. The algorithm showed that i.v. Ca gluconate 8 g/150 dL (5% glucose)/day was administered for Ca levels <6.5 mg/dL, 4–6 g/75 dL/day for levels <7.6 mg/dL, and 2 g/15 dL/15 min for symptomatic hypocalcemia. Young age, low Ca, and high Alk-ptase levels and long operation time were independent risk factors for severe hypocalcemia. Serum Ca levels <7.6 mg/dL at 18 h post-operation were the optimal cutoff value for hypocalcemia that needed i.v. Ca gluconate. The post-operative hospitalization in Group B was 3–5 days shorter than that previously reported. The readmission rate (0.62%) due to hypocalcemia was rare.

**Keywords:** secondary hyperparathyroidism, total parathyroidectomy plus autotransplantation, severe hypocalcemia, intravenous calcium gluconate
