P79 - ECE_2596 - Predicting permanent postoperative hypoparathyroidism using preoperative and intraoperative PTH dynamics

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Abstract Background Permanent postoperative hypoparathyroidism (PpoHypoPT) is a clinically significant complication of total thyroidectomy, associated with renal morbidity and long-term deterioration in quality of life. Early identification of patients at risk among those who initially develop postoperative hypoparathyroidism (poHypoPT) may enable optimized management strategies. This study investigates preoperative, intraoperative, and early postoperative determinants of progression to PpoHypoPT. Methods We conducted a retrospective analysis involving 295 patients who developed poHypoPT following total thyroidectomy between 2015 and 2022. PpoHypoPT was defined as persistent dependence on calcitriol to maintain asymptomatic normocalcaemia or failure to achieve serum PTH >15 pg/mL at any point during follow-up, despite supplementation with calcifediol and calcium. Patients recovering PTH >15 pg/mL without calcitriol were classified as having transient poHypoPT (TpoHypoPT). Clinical characteristics, perioperative biochemical parameters, intraoperative findings, and postoperative PTH kinetics (immediate and 24-hour values) were compared. Independent predictors were identified using multivariate logistic regression. Results Of the 295 patients with poHypoPT, 52 (17.6%) progressed to PpoHypoPT, corresponding to an overall incidence of 6.8% among 767 total thyroidectomies. PpoHypoPT was associated with older age, lower postoperative calcium levels and reduced immediate and 24-hour postoperative parathyroid hormone (PTH) concentrations. It was also associated with the identification of fewer than three parathyroid glands during surgery. Central neck dissection did not increase risk. In multivariate analysis, age, number of identified parathyroid glands, preoperative PTH, and the 24-hour PTH/baseline PTH ratio were independent predictors. Identification of fewer than three parathyroid glands was the strongest predictor of PpoHypoPT (OR 4.81). PTH at 24 hours showed the highest diagnostic performance (AUC 0.798). A 24-hour PTH threshold of 6.5 pg/mL optimally predicted PpoHypoPT (with a sensitivity of 56.3% and a specificity of 89.2%). Conversely, a PTH24h decline of less than 86.3% from baseline predicted the recovery of parathyroid function (sensitivity: 54.3%; specificity: 86.5%). Conclusions The incidence of PpoHypoPT after total thyroidectomy was 6.8%, occurring in 17.6% of patients with poHypoPT. Intraoperative identification of fewer than three parathyroid glands was found to be the most powerful predictor of permanent dysfunction. Higher preoperative PTH levels were also associated with increased risk, underscoring the potential relevance of preoperative vitamin D optimization. Early postoperative PTH dynamics, particularly PTH24h below 6.5 pg/mL or a reduction of over 86% from baseline, provide robust markers of the progression to permanent hypoparathyroidism.

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