Elevation of serum parathyroid hormone (PTH) with normocalcemia after parathyroidectomy for primary hyperparathyroidism (pHPT) has been documented. This study was performed to investigate the factors correlated with elevated PTH level after surgery.

Twenty-one patients who underwent successful parathyroidectomy for pHPT had elevated postoperative serum PTH level despite normocalcemia. Patients were categorized into 2 groups based on their serum PTH level: patients who had fluctuation between normal and elevated PTH (group 1, n=12) and patients with early elevated PTH levels, and then normalized during follow up (group 2, n=6). Serum level of PTH, total calcium, ionized calcium, alkaline phosphatase, creatinine, vitamin D, osteocalcin and bone densitometry were compared before and after surgery. Three patients with persistently elevated PTH showed impaired renal function and they were excluded from this analysis.

There were no difference in total calcium and ionized calcium (8.84±0.44 mg/dl vs. 8.74±0.32 mg/dl, 4.66±0.20 mg/dl vs. 4.56±0.31 mg/dl) between two groups. In comparison of variable group and normalized group, tumor size, 2.36 ±1.29 cm vs. 1.80±0.34 cm; preoperative PTH level, 418.18 ±488.90 pg/ml vs. 281.33±44.39 pg/ml; alkaline phosphatase levels, 369.36±570.80 IU/L vs. 202.17±115.63 IU/L; increment of bone densities of lumbar spine and femur, 18.32± 18.55% vs. 12.08±12.26%, 12.54±19.05% vs. 4.17± 5.03%; vitamin D level, 24.68±12.98 ng/ml vs. 31.22± 13.88 ng/ml; osteocalcin level is 15.71±5.33 ng/ml vs. 37.03±15.00 ng/ml. In 3 patients with creatinine level 4.00 ±3.64 mg/dl showed impaired renal function and their PTH level was persistently elevated.

Patients with more advanced pHPT showed more variable postoperative PTH level than patients with normalized PTH level, although statistically insignificant due to small numbers. Patients with persistently elevated PTH level would be considered possibility of impaired renal function.