The Timing of Parathyroid Hormone Measurement as an Early Predictor of Postoperative Hypocalcemia Post Total Thyroidectomy: A Prospective Study

Abstract Background: Serum intact parathyroid hormone (iPTH) level is an early marker of post-thyroidectomy hypocalcemia. However, lack of methodological standardization to define timing and cut-off points of iPTH measurement limit its clinical applicability. Here, we evaluated the relationship between two distinct postoperative time sampling and iPTH accuracy on predicting hypocalcemia. Aim of Study: This study was aimed to evaluate the accuracy of iPTH measured after total thyroidectomy to predict postoperative hypocalcemia and to identify patients at risk of postoperative hypocalcaemia who require supplementation treatment, and those not at risk who can be safely discharged without any supplementation treatment. Moreover, combining postoperative PTH and serum calcium levels could result in an accurate prediction of the risk of postoperative hypocal-caemia. Patients and Methods: iPTH was measured within 24h after surgery (iPTH 24h) and on the morning of the 3rd postoperative day (iPTH 3rd PO). Hypocalcemia was defined by levels of total calcium corrected by serum albumin £8.0mg/dL and/or by the presence of symptoms or signs. The most accurate iPTH cut-off point for hypocalcemia prediction was established from a ROC curve comparing both time-points. Results: The study included 40 patients. The mean age was 46.23±9.03 years, 34 were women (85%) and all patients underwent total thyroidectomy. Hypocalcemia occurred in 8 patients (20%), of whom 5 were symptomatic. Lower levels of iPTH 24h and iPTH 3rd PO were associated with postop-erative hypocalcaemia (p < 0.05). Using the ROC curve, the optimal cut-off points were 14.8pg/mL and 14pg/mL for iPTH 24h and iPTH 3rd PO, respectively. The comparison of the AUC showed no significant difference between these two points of evaluation with 98% accuracy for both time points. Conclusions: Serum iPTH levels measured within 24h or on the 3rd morning after surgery are predictors of postoperative hypocalcemia. Notably, both time-points have the same accuracy to predict postoperative hypocalcemia (with different cutoff points).