Is perioperative drop in PTH better than postoperative PTH in predicting hypocalcaemia after thyroid surgery?

Postoperative surgical hypoparathyroidism (PoSH) following thyroid surgery is well known complication. Several predictive factors have been identified including perioperative parathyroid hormone (PTH) levels. The aim of the study is to determine how a drop in perioperative parathyroid hormone (PTH) compares to postoperative day one PTH in predicting hypocalcaemia. Methods Medical records of consecutive patients who had either total or completion thyroidectomy with or without central neck dissection between January 2016 and December 2018 in a single thyroid surgery unit were accessed to retrieve data on demographics, pathology, surgery, perioperative biochemistry and management. Results Of 295 included patients, there were 227 (76.9%) females. Forty-five (15.3%) had completion thyroidectomy, while the rest had total thyroidectomy. Seventy-eight (26.4%) had concomitant central neck dissection. 64 (21.7%) had day 1 hypocalcaemia and this was persistent at six months in 31 patients (10.5%). Both day one PTH and drop in PTH predicted day one hypocalcaemia (P<0.001) and 6-month hypoparathyroidism (p<0.001). The area under ROC curves for day one PTH and drop in PTH for day one hypocalcaemia (0.729 vs 0.726 respectively) and for 6-month hypoparathyroidism (0.964 vs 0.958 respectively) were similar; albeit slightly better for day 1 PTH. Conclusion Day 1 PTH is equivalent to (if not better than) drop in PTH in predicting short and long term PoSH. Preoperative PTH measurements are therefore not needed in detection and/or management of PoSH after thyroid surgery.