Objective:To observe the relationship between the occurrence of symptomatic hypocalcemia (SH) and various potential influencing factors in patients after thyroidectomy, stratify according to the scope of thyroidectomy, and explore the predictive value of intact parathyroid hormone (iPTH) for postoperative SH.Methods:Among 3 379 patients with thyroidectomy who admitted into the First Affiliated Hospital of Zhengzhou University from January 2020 to February 2021, 122 patients with SH after thyroidectomy were collected retrospectively and set as SH group. 100 patients of the remaining 3 200 patients who did not suffer from SH in the same year were selected by systematic sampling method and set as control group. Pearson correlation analysis was used to analyze the potential influencing factors such as age, preoperative calcium, postoperative calcium, preoperative iPTH, postoperative iPTH, central lymph node number, blood loss, operation duration, gender, lymph node dissection method, thyroidectomy range, postoperative pathological type and other. Among them, the measurement data of normal distribution were expressed by mean±standard deviation( Mean± SD), t-test was used for the comparison between the two groups, and Chi-square test was used for count data. By drawing the receiver operating characteristic curve (ROC), the iPTH levels in patients with and without SH before/after operation (different surgical methods) were studied, and the diagnostic threshold, sensitivity and specificity of iPTH were predicted. Results:Among 3 379 patients, 122 patients suffered from SH after thyroidectomy, with the incidence rate of 3.6%. There were significant differences in gender (8 males and 114 females in SH group; 27 males and 73 females in control group), whether lateral area dissection was performed (58 cases with dissection and 64 cases without dissection in SH group; 7 cases with dissection and 93 cases without dissection in control group), thyroidectomy range (14 cases with one side and 108 cases with both sides in SH group; 73 cases with one side and 27 cases with both sides in control group), age (40.1 years old vs 43.2 years old), dissection number of central lymph nodes (8.6 vs 4.6), dissection number of cervical lymph nodes (12.3 vs 0.7), blood loss (22.8 mL vs 11.0 mL), operation duration (1.7 h vs 0.8 h), postoperative iPTH (16.4 pg/mL vs 41.9 pg/mL), preoperative iPTH (39.4 pg/mL vs 47.8 pg/mL) in SH group; and postoperative calcium level (1.9 mmol/L vs 2.2 mmol/L). There was significant differences between the two groups ( P<0.05). However, there was no significant differences between them with postoperative pathological type (4 cases with toxic goiter, 3 cases with medullary thyroid carcinoma, 1 case with thyroid follicular carcinoma, 114 cases with papillary thyroid carcinoma in SH group; 1 case with medullary thyroid carcinoma, 1 case of thyroid follicular carcinoma, 98 cases with papillary thyroid carcinoma in control group, P=0.25) and preoperative calcium (2.3 mmol/L vs 2.3 mmol/L, P=0.10). For patients with bilateral thyroidectomy, SH was easy to occur when postoperative iPTH < 20.08 pg/mL, and its sensitivity and specificity were 74.07% and 96.30%; however, for patients with unilateral thyroidectomy, SH was easy to occur when iPTH < 24.00 pg/mL after operation. Conclusions:Gender, age, postoperative calcium, preoperative iPTH, postoperative iPTH, central lymph node number, blood loss, operation duration, lymph node dissection method and thyroidectomy range are important factors affecting the occurrence of SH after thyroidectomy. With the expansion of surgical range, the postoperative iPTH level gradually decreases, which predicts the occurrence of symptomatic hypocalcemia. In order to avoid the occurrence of symptomatic hypocalcemia after operation, it is necessary to supplement calcium in time according to the range of operation and postoperative iPTH level.