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.