Optimal cutoff values of intraoperative parathyroid hormone for predicting early and permanent hypoparathyroidism after total thyroidectomy

Abstract

Purpose: Measurement of intraoperative intact parathyroid hormone (ioPTH) levels is a reliable predictor of postsurgical hypocalcemia. We assessed the optimal cutoff values of ioPTH decline for predicting postoperative early and permanent hypoparathyroidism. Methods: This was a retrospective study of a prospectively maintained database of patients undergoing thyroid surgery in a tertiary care hospital in L'Hospitalet de Llobregat (Barcelona, Spain). All consecutive patients undergoing total thyroidectomy with or without central neck dissection between January 2005 and May 2021 were analyzed. The best cutoff value of the decrease of ioPTH level between PTH assessed after induction of anesthesia and at 10 min after completion of surgery for predicting hypocalcemia was evaluated. Results: We included 742 patients (mean age 52 years) (thyroid cancer 48%, neck dissection 42%) undergoing total thyroidectomy. Postoperative hypocalcemia was diagnosed in 383 (51.6%) patients, which was transient in 296 (39.9%) and permanent in 87 (11.7%). The optimal cutoff value for predicting transient hypocalcemia was a decline of ioPTH level of ≤ 62.5% (overall efficacy 87%), but calcium supplementation may be indicated in high-risk cutoff values of ≥ 79.9%. In patients with an ioPTH decline ≤ 39%, the probability of postoperative hypocalcemia is extremely unlikely. Patients with declines > 93.7% should be followed very closely since they are high-risk for developing permanent hypoparathyroidism. Conclusion: The decline of ioPTH, measured as the difference between ioPTH before thyroidectomy and after completion of the surgical procedure is a reliable indicator of the likelihood of postoperative transient hypocalcemia, with optimal cutoff value of 62.5%.