Percentage Decline of Parathyroid Hormone Level is a Predictor for Post-thyroidectomy Symptomatic Hypocalcemia

Purpose: Postoperative hypocalcemia is one of the most common complications after thyroid surgery. However, the predictive efficacy of parathyroid hormone (PTH) level was still controversial. We investigated the cut-off value of perioperative PTH level for postoperative hypocalcemia after total thyroidectomy. Methods: Four hundred eighty-two patients performed total thyroidectomy from January 2015 to December 2016 were enrolled. Demographics, operative variables and the development of symptomatic hypocalcemia were collected and evaluated. Results: Transient symptomatic hypocalcemia occurred in 83 (17.2%) patients and 5 (1.0%) patients have progressed to the permanent hypocalcemia. Patients with transient symptomatic hypocalcemia showed significantly lower postoperative day 1 PTH level than those without hypocalcemia (7.7±6.5 vs. 13.1±10.4 pg/mL; P<0.001), while correlation between postoperative PTH level and development of symptomatic hypocalcemia was not found in a multivariate analysis (P=0.122). Percentage decline of the preoperative PTH only showed significant association with transient hypocalcemia and the recommended cut-off value was 75.0%. When percentage decline of 75.0% was used, the incidence of transient hypoparathyroidism was 3.4 times (95% confidence interval, 2.1-5.6) higher in high percentage decline group (P<0.001). In regard to the permanent hypoparathyroidism, there were no significant differences in all factors. Conclusion: Percentage decline of PTH can be used as a predictive factor for postoperative hypocalcemia. Cautions against preventing injury of the parathyroid glands with careful surgical technique should be recommended.