Early prediction of hypocalcemia following total thyroidectomy using combined intact parathyroid hormone and serum calcium measurement

Backgrounds Concomitant intact parathyroid hormone (iPTH) and serum calcium measurement is deemed to be useful in predicting hypocalcemia after total thyroidectomy. This study aimed to prospectively assess the diagnostic accuracy of combined iPTH and serum calcium measurement in predicting early postoperative hypocalcemia. Methods From January 2010 to January 2011, 112 patients underwent total thyroidectomy in our department. A prospective study was carried out to search for factors predicting postoperative hypocalcemia. Serum calcium, phosphorus, and iPTH levels have been measured before operation and at 6, 24, and 48 h postoperatively. Hypocalcemia was defined as a serum calcium level less than 8.0 mg/dL. Sensitivity and specificity of different serum measurements have been calculated using the receiver–operator characteristics curve. Results Thirty-three patients (29.5 %) had transient postoperative hypocalcemia. Serum iPTH level showed the highest sensitivity and specificity in predicting hypocalcemia after 6 h (84.8 % and 93.7 %, respectively) for a criterion value ≤12.1 pg/mL. Serum calcium level showed the highest sensitivity and specificity after 24 h (93.9 and 100.0 %, respectively) for a criterion value ≤7.97 mg/ dL. Combined cutoffs of 6-h iPTH and 24-h serum calcium showed sensitivity and specificity of 100.0 %. Conclusions The combined measurement of 6-h iPTH and 24-h serum calcium are highly predictive of early postoperative hypocalcemia. Patients with serum iPTH and calcium level≤criterion value are at major risk for developing hypocalcemia. These results are important in selecting patients eligible for early discharge and those patients who need calcium and vitamin D supplementation.