Normocalcemia with elevated parathyroid hormone levels after surgical treatment of primary hyperparathyroidism

BACKGROUND: Thirty percent of patients who undergo successful parathyroidectomy for primary hyperparathyroidism show unexplained elevated postoperative serum parathyroid hormone (PTH) levels despite normocalcemia. METHODS: PTH levels were measured monthly in 97 patients for 6 months after parathyroidectomy. Renal function, 25-OH-vitamin D levels, serum alkaline phosphatase levels, osteocalcin, and bone densitometry were evaluated before and 6 months after surgery. PTH reactivity to calcium loading was tested at the sixth month. RESULTS: Thirty patients had elevated PTH levels despite normocalcemia after parathyroidectomy. Before surgery, these 30 patients had higher PTH and creatinine levels, lower vitamin D levels, and more extensive bone involvement than those with normal postoperative PTH levels. In patients with normal renal function and normal vitamin D levels, postoperative PTH values correlated with preoperative PTH levels but not with bone disease. CONCLUSION: In most cases, elevated PTH levels after surgery is an adaptive reaction to renal dysfunction or vitamin D deficiency. If no adaptive cause can be found, persistent hyperparathyroidism must be suspected.