The patients were monitored for postoperative biochemical hypocalcemia at 12, 24, 48, and 72 h postoperatively (during hospitalization and after discharge on morning outpatient visits), with hypocalcemia being defined as a total serum calcium level lower than 2.0 mmol/L, in either asymptomatic or symptomatic patients. Persistent hypocalcemia for more than 6 months after the operation was regarded as permanent hypoparathyroidism.