OC10.3 - ECE_2879 - Dynamic postoperative PTH as a strong predictor of hypoparathyroidism after total thyroidectomy: a large cohort analysis

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Abstract Background Postoperative hypoparathyroidism (poHypoPT) is a frequent complication of total thyroidectomy. Its early identification is clinically relevant, and postoperative PTH dynamics—particularly the 24-hour decline—have emerged as strong predictors. poHypoPT is best defined as an undetectable or inappropriately low postoperative PTH level in the presence of hypocalcaemia, with or without symptoms. This study evaluates its incidence and predictive factors in a large surgical cohort. Methods We retrospectively analysed patients who underwent total thyroidectomy, with or without central neck dissection (CND), between 2016 and 2022. poHypoPT was defined by at least one of the following: (a) corrected calcium (CorCa) <7.5 mg/dL; (b) CorCa <8.0 mg/dL with simultaneous PTH <15 pg/mL during postoperative admission; (c) hypocalcaemic symptoms resolving with oral or intravenous calcium during admission or after discharge; or (d) PTH <10 pg/mL at 24 hours. Variables included demographics, thyroid function, surgical characteristics, intraoperative parathyroid identification, and postoperative PTH dynamics (baseline, immediate, and 24-hour values). Results A total of 768 patients were included (79.7% women; median age 54 years). Hyperthyroidism (TSH <0.1) was present in 19.3%. CND was performed in 25%, and malignancy was suspected or confirmed preoperatively in 50%. poHypoPT occurred in 296 patients (38.5%). It was associated with younger age, lower BMI, female sex, surgery for suspected/confirmed malignancy, CND, greater immediate and 24-hour postoperative declines in PTH, total calcium and CorCa, and larger gland size by specimen weight. In multivariate analysis excluding calcium and PTH values (diagnostic criteria), age, sex, and postoperative PTH dynamics remained independent predictors. When PTH dynamics were excluded, CND was the strongest predictor (OR 3.58; IC95: 2.49- 5.18). PTH at 24 hours (PTH24H) showed the highest diagnostic accuracy (AUC 0.930). A PTH24h >17.5 pg/mL predicted a 93.3% probability of not developing poHypoPT, while a reduction <68.8% from baseline predicted its absence with 96.37% sensitivity and 80.9% specificity with a predictive negative value of 97.3%. Conclusions Using strict biochemical and clinical criteria, poHypoPT incidence reached 31.5%. Lower BMI and female sex were modest predictors. Postoperative PTH dynamics—particularly a 24-hour PTH >17.5 pg/mL or a decline <70% from baseline—demonstrated excellent negative predictive value and are reliable tools for early risk stratification after total thyroidectomy.

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