Determinants of postoperative hypocalcemia in vitamin D–deficient Graves’ patients after total thyroidectomy

Abstract

Background The etiology of postoperative hypocalcemia after total thyroidectomy appears to be multifactorial, that is, postoperative transient hypoparathyroidism, low 25-hydroxy vitamin D (25-OHD) concentrations, aging, and hyperthyroidism with increased bone turnover. Our aim was to evaluate the factors responsible for postoperative hypocalcemia in euthyroid vitamin D–deficient/insufficient Graves patients who underwent total thyroidectomy at our institution. Methods Thirty-five consecutive patients with Graves disease treated by total thyroidectomy were included in the present study. All patients were vitamin D deficient/insufficient (ie, 25-OHD concentrations of <20/<30 ng/mL, respectively). Patients were divided into 2 groups according to postoperative serum albumin corrected calcium concentrations: group 1 (n = 13) patients had postoperative serum calcium concentrations of 8 mg/dL or less; group 2 (n = 22) patients had serum calcium concentrations greater than 8 mg/dL. Bone turnover markers (deoxypiridinoline, bone-specific alkaline phosphatase) and 25-OHD were determined the day before surgery. Results In group 1 patients, disease duration was significantly longer, 25-OHD and postoperative parathyroid hormone concentrations were significantly lower, and bone turnover markers were significantly higher. Logistic regression analysis revealed that a postoperative parathyroid hormone concentration less than 10 pg/mL was the most powerful parameter to predict postoperative hypocalcemia (odds ratio, 23; 95% confidence interval, 3.3–156). Conclusions In Graves patients with vitamin D deficiency/insufficiency, postoperative (transient) hypoparathyroidism is the most significant parameter to determine the development of postoperative hypocalcemia.