Predictive Value of Intraoperative Parathyroid Hormone for Hypocalcemia following Total Thyroidectomy

Abstract

Objectives: Investigate whether intraoperative parathyroid hormone (PTH) can predict postoperative hypocalcemia following total thyroidectomy. Methods: Cohort study with chart review of total or completion thyroidectomy patients in academic and private settings from May 2013 to February 2014. A total of 42 patients who underwent total thyroidectomy with or without central node dissection were enrolled prospectively. PTH were measured at 2 time points: preincision after induction of general anesthesia and postexcision 20 to 30 minutes following total thyroidectomy. Serum calcium was measured at midnight after surgery (6 hours) and the next morning at 6 am (12 hours). Changes in intraoperative PTH were correlated with post-thyroidectomy serum calcium. Results: Preincision PTH did not show any correlation with 6-hour calcium. Postexcision PTH values stratified in an interval of 50 were not associated with significantly different calcium levels (PTH 50-99.9, Ca 8.2; 100-149.9, 8.4; 150-199.9, 8.2). Patients with PTH less than 50 had a decreased mean calcium at 7.7; however the reduction was not statistically significant ( P = .143). The reduction from preincision to postexcision PTH between 75% and 99.9% was associated with hypocalcemia (mean Ca 7.5; P = .041). However, a reduction less than 75% did not yield significant decreases in calcium (percentage reduction 0% to 24.9%, Ca 8.2; 25% to 49.9%, 8.2; 50% to 74.9%, 8.2). Conclusions: Preincision PTH is not a reliable predictor of postoperative hypocalcemia. A decrease of 75% or more in PTH following total thyroidectomy is more likely to result in postoperative hypocalcemia.