Are Patients Undergoing Thyroidectomy in Montreal, Canada, during Winter at Increased Risk for Postoperative Hypocalcemia?

Abstract

Objectives: (1) Review the rate of postoperative hypocalcemia in patients undergoing thyroidectomy in the summer and winter. (2) Identify the association between the season when surgery was completed and the risk of postoperative hypocalcemia. Methods: A retrospective chart review of 436 patients undergoing thyroidectomy at the McGill University Thyroid Cancer Centre from 2006 to 2014 was performed. Patients undergoing total or completion thyroidectomy in the winter months (December to February) and summer months (July to September) were included in the study. Parathyroid hormone (PTH) and serum corrected calcium were recorded according to the McGill post-thyroidectomy protocol. Preoperative PTH and 25-hydroxyvitamin D (25-OHD) were measured. Hypocalcemia was defined as a corrected calcium level <1.9 mmol/L. Results: The rate of postoperative hypocalcemia was 8% for patients operated on in the winter and 1.8% for those in the summer ( P = .01). Patients undergoing surgery in the winter were 4.3 times more likely to develop postoperative hypocalcemia than those in the summer ( P = .01, 95% confidence interval [1.5 to 1 5]). Surgery during the summer months showed a higher preoperative 25-OHD level ( P = .04). Preoperative PTH levels were significantly greater in the winter months as compared with the summer (5 pmol/L and 4.5 pmol/L, respectively; P = .01). Patients with 25-OHD deficiency (≤70nmol/L) were not found to have a higher rate of postoperative hypocalcemia (5.2% and 13.8%, respectively; P = .22). Conclusions: In this study, patients undergoing thyroidectomy during the winter months were 4.3 times more likely to develop postoperative hypocalcemia when compared with patients operated in the summer.