Elevated parathyroid hormone levels in normocalcemic patients after parathyroidectomy for primary hyperparathyroidism: what risk factors should be considered?

OBJECTIVE: Normocalcemia with elevated parathyroid hormone levels (NCePTH) after successful parathyroidectomy in patients with primary hyperparathyroidism (PHPT) has drawn attention during the postoperative period and remain a clinical conundrum. PATIENTS AND METHODS: We retrospectively studied 539 consecutive patients with PHPT who underwent parathyroid surgery from August 2017 to December 2023. RESULTS: The mean age of the patients was 53.3 years, and 66.3% of the patients were female. After a median follow-up of 12 months, 9.9% of the patients were diagnosed with NCePTH. Compared with patients who were cured after surgery, those with NCePTH had high preoperative serum PTH levels (median [quartile], 228 pg/mL [126, 387] vs. 150 pg/mL [108.65, 251.5], p = 0.039) and PTH levels on the first postoperative day (median [quartile], 23.5 pg/mL [8.1, 35.6] vs. 9.7 pg/mL [4, 21.15], p = 0.000). Patients with NCePTH after surgery did not differ from those with normal PTH levels in terms of sex, age, body mass index, history of thyroid/parathyroid surgery, calcium, phosphorus, and creatinine levels and parathyroid lesion size. According to the multivariable analysis, a preoperative PTH concentration ≥ 191 pg/mL (odds ratio [OR], 8.78; p = 0.003) and PTH concentration ≥ 16.4 pg/mL (odds ratio [OR], 12.47; p = 0.0004) on the first day after surgery remained risk factors for NCePTH. CONCLUSIONS: The incidence rate of NCePTH after successful parathyroidectomy in patients with PHPT was 9.9%. A preoperative PTH concentration ≥ 191 pg/mL and a PTH concentration ≥ 16.4 pg/mL on the first day after surgery were identified as risk factors for NCePTH after parathyroidectomy. CLINICAL TRIAL NUMBER: Not applicable.