Parathyroid hormone decline 4 hours after total thyroidectomy accurately predicts hypocalcemia

Background: The level of parathyroid hormone (iPTH) serum has been controversial in the prediction of postthyroidectomy hypocalcemia. Analysis of the decrease between preoperative and postoperative iPTH levels should be more accurate. Therefore, the aim of our study was to prospectively establish the reliability of the iPTH decrease for early diagnosis of postoperative hypocalcemia and to identify the patients who are not at risk for hypocalcemia.

Methods: A prospective study of 137 consecutive patients who underwent total thyroidectomy was performed. Serum iPTH level was measured preoperatively and 4 hours postoperatively (iPTH(H4)). The sensitivity, specificity, and positive and negative predictive values for the iPTH(H4) and for the iPTH decline were estimated by confidence interval from thresholds determined by ROC curve analysis.

Results: Thirty-nine patients developed hypocalcemia (28.5%). Patients who developed hypocalcemia had a significantly lower iPTH(H4) and a significantly greater iPTH decrease (P < .001). The thresholds enabling prediction of hypocalcemia were 19.4 ng/L for iPTH(H4) and 68.5% for iPTH decline. Sensitivity, specificity, and positive and negative predictive values for iPTH(H4) were 84.6%, 92.9%, 82.5%, and 93.8% (overall accuracy, 90.5%). iPTH decline was more accurate to predict hypocalcemia (sensitivity, 97.4%; specificity, 95.9%; positive predictive values 90.5%; negative predictive values, 98.6%; and overall accuracy, 96.4%).

Conclusion: The decrease in iPTH is more precise than the iPTH(H4) alone and can accurately predict hypocalcemia after total thyroidectomy. Patients with a decrease in iPTH less than 68.5% can be discharged at postoperative day one without any supplementation. Patients with iPTH decline more than 68.5% should be administered calcium and vitamin D supplementation before symptoms appear.