Perioperative parathyroid hormone levels in thyroid surgery

OBJECTIVE: Perioperative hypocalcemia from temporary parathyroid gland dysfunction is common after thyroid surgery. No reliable cutoff values for parathyroid hormone (PTH) and the subsequent possibility of developing hypocalcemia exist. The purpose of this study is to determine a criterion for predicting hypocalcemia based on different PTH levels as cutoff values. STUDY DESIGN: Retrospective chart review. METHODS: A centralized database of intraoperative PTH levels was analyzed. PTH values approximately 10 minutes after excision of the thyroid gland and in the recovery room were obtained; serial ionized calcium levels were also analyzed. PTH values were then compared using chi-square analysis with significance defined as P < .05. A receiver operator characteristic (ROC) curve was also constructed to define sensitivities and specificities of different PTH levels as potential cutoff values. RESULTS: Eighty patients were identified meeting the study criteria between January 1999 and February 2005. Fourteen of the 80 (17.5%) patients became hypocalcemic during the hospital stay; none experienced permanent hypocalcemia. Patients who became hypocalcemic during their hospitalization were more likely to have a PTH level below 15 pg/mL (P < .01). Patients with a PTH level less than 15 pg/mL were more likely to develop hypocalcemia (P < .01). Finally, an ROC curve was constructed, allowing the surgeon to determine acceptable sensitivities and specificities and various PTH cutoff values. CONCLUSION: Low perioperative PTH levels significantly correlate with the presence of postoperative hypocalcemia but cannot be used to predict it. Using the ROC curve allows different chosen cutoff values to predict hypocalcemia with varying sensitivity and specificity.