Early prediction of symptomatic hypocalcaemia after total thyroidectomy using 2-hour postoperative parathormone dynamics

Objectives: Thyroid diseases are the commonest endocrine disorders worldwide. Hypocalcaemia remains the most common complication and the reason for prolonged hospitalisation following total thyroidectomy. Serum parathormone (PTH) levels have long been used to predict post-thyroidectomy hypocalcaemia, but consensus on the timing and utility of PTH remains elusive. This study aims to evaluate the association between symptomatic hypocalcaemia and serum parathormone levels (preoperative and 2-hour postoperative values). Material and Methods: This is a prospective study of 107 patients who underwent Total thyroidectomy +/- lymph node dissection at a tertiary care teaching hospital during the period from March 2023 to October 2024. PTH was measured preoperatively and 2 hours post thyroidectomy. PTH decline percentage was calculated based on the pre- and postoperative PTH values [(preoperative PTH-postoperative PTH)/preoperative PTH x 100]. Calcium and phosphorus were measured on postoperative day 1. Receiver operating characteristic (ROC) analysis was used to determine optimal cut-off values. Multivariate logistic regression was performed to identify independent predictors of symptomatic hypocalcaemia. Results: A PTH decline >71.75%, postoperative PTH <11.3 pg/ml and postoperative calcium value <8.51mg/dl significantly predicted symptomatic hypocalcaemia. PTH decline percentage was the variable with the highest area under the ROC curve (0.926), followed by the absolute postoperative PTH value (0.898), postoperative corrected calcium value (0.734) and postoperative phosphorus (0.659). On multivariate logistic regression, percentage PTH decline (OR 1.08 per 1% decline, p = 0.002), postoperative corrected calcium (OR 0.12, p = 0.009), and central compartment neck dissection (OR 18.14, p = 0.018) were found to be independent predictors of symptomatic hypocalcaemia. Conclusion: 2 hours post-thyroidectomy, PTH decline percentage is a strong and independent predictor of symptomatic hypocalcaemia, outperforming absolute postoperative PTH levels. PTH decline percentage of ≥ 50% (sensitivity = 98.04%) and a decline of ≥ 90% (specificity = 96.43%) can be used as rule-out and rule-in tests, respectively, for discharging patients and can guide calcium supplementation.