Hypothesis: Combined measurement of intact parathyroid hormone (iPTH) and serum calcium (sCa) levels is useful for predicting postoperative hypocalcemia with minimal laboratory effort and low costs.
Design: Prospective analysis of 170 consecutive patients.
Setting: University hospital referral center.
Patients: One hundred seventy patients underwent total thyroidectomy. Defining hypoparathyroidism as albumin-adjusted sCa levels of less than 1.9 mmol/L with or without clinical symptoms or subnormal sCa levels (1.9-2.1 mmol/L) with neuromuscular symptoms, the influences of central lymph node dissection, experience of the surgeon, and parathyroid autotransplantation were observed. We measured the sCa and iPTH levels separately and in combination and the postoperative sCa slope to predict patients who were at risk of hypoparathyroidism.
Main outcome measures: Predictive values for iPTH and sCa levels were compared to identify postoperative hypoparathyroidism.
Results: Of the 170 study patients, 41 developed transient hypoparathyroidism and 2 developed permanent hypoparathyroidism. The morphologic features and function of the thyroid gland, central neck dissection, experience of the surgeon, and parathyroid autotransplantation did not influence development of postoperative hypoparathyroidism. The best sensitivity for predicting postoperative hypoparathyroidism was 97.7% for measurement of iPTH levels, and the best specificity was 96.1% for measurement of sCa levels. Negative and positive predictive values reached their best (99.0% and 86.0%, respectively) when we combined sCa and iPTH values.
Conclusions: Patients with iPTH levels of 15 pg/mL or less and sCa levels of 1.9 mmol/L or less are at increased risk of developing postoperative hypoparathyroidism. Measuring iPTH levels 24 hours after total thyroidectomy in combination with sCa levels on the second postoperative day allows the prediction of hypoparathyroidism with a high sensitivity, specificity, and positive predictive value.