The dynamic changes and precise classification of parathyroid function within one year after thyroid cancer surgery

Background: Postoperative parathyroid dysfunction is a common complication of thyroid surgery. However, the temporal pattern of postoperative parathyroid function and standardized clinical interventions remain poorly defined. This study systematically characterizes the dynamic changes in postoperative parathyroid hormone (PTH) following thyroid cancer surgery and proposes a clinically applicable classification system with corresponding management strategies. Materials and methods: A total of 12,664 patients who underwent thyroid cancer surgery between 2012 and 2022 across three tertiary hospitals were included. Changes in postoperative PTH were analyzed using locally estimated scatterplot smoothing regression. Logistic regression analysis was performed to identify independent risk factors associated with different postoperative PTH trajectories. Results: Based on 38,949 postoperative PTH measurements from 12,664 patients, we observed that PTH levels declined sharply after surgery, reached the lowest point around one week (defined as valley value PTH, vvPTH), then rose rapidly and stabilized after one month (defined as new baseline PTH, nbPTH). Importantly, postoperative PTH did not fully recover to preoperative levels. Five distinct postoperative PTH trajectory types were identified based on vvPTH and nbPTH: I (normal function), II (subclinical injury), IIIA (sufficiently recovered hypoparathyroidism), IIIB (insufficiently recovered hypoparathyroidism), and IIIC (refractory hypoparathyroidism). Multivariate analysis identified operation type, lymph node dissection, parathyroid autotransplantation, and preoperative PTH as independent predictors, which were integrated into a predictive nomogram. Patients with type III disease require intensive monitoring and calcium supplementation within the first month, whereas type IIIC patients require long-term management. Conclusion: Parathyroid function does not fully return to preoperative levels within one year after thyroid surgery. This large-scale study establishes a precise classification system for postoperative parathyroid function, which may provide a valuable framework to guide clinical management and optimize patient outcomes.