Predictors and risk factors of hypoparathyroidism after total thyroidectomy.

Background: The aim of this study was to evaluate the risk factors for hypoparathyroidism after total thyroidectomy and to determine whether early postoperative serum levels of calcium and phosphorus could be used to predict its development.

Materials And Methods: The study group consisted of 1030 patients who had undergone total thyroidectomy at our institution between March 2008 and July 2014. The clinicopathologic characteristics, indications for the operation, and surgical details of normocalcemic and hypocalcemic patients were compared, and variations in serum calcium and phosphorus levels were measured every day after the operation.

Results: Of the 1030 patients, 291 (28.2%) were found to have transient hypocalcemia and 27 (2.6%) had permanent hypocalcemia. On univariate analysis, younger age (P = 0.001), female gender (P < 0.001), longer operative time (P = 0.009), extent of central neck dissection (CND) (P = 0.003), and malignancy (P = 0.005) were found to be significantly associated with transient hypocalcemia. On multivariate analysis, female gender (P = 0.001), extent of CND (P = 0.017), and the identification of parathyroid gland (PTG) tissue in permanent pathologic sections were significant factors. In addition, the occurrence of postoperative hypocalcemia was correlated with relative changes in serum calcium and phosphorus levels. Patients whose serum calcium levels decreased over 20% on postoperative day 2 were more likely to develop hypoparathyroidism, with 92% specificity.

Conclusion: Female gender (P = 0.001), extent of CND (P = 0.014), and PTG in permanent pathologic sections (P = 0.035) were found to be significant factors affecting the development of hypocalcemia. Despite some study limitations, we suggest that the relative changes in the serum levels of calcium (20%) and of phosphorus (40%) on the second postoperative day may be reliable predictors of post-thyroidectomy hypoparathyroidism.