Elevated serum parathyroid hormone concentration in eucalcemic patients after parathyroidectomy for primary hyperparathyroidism and its relationship to vitamin D profile.

Elevation of serum parathyroid hormone (PTH) level in eucalcemic patients after parathyroidectomy for primary hyperparathyroidism has been described in up to 40% of patients, but little is known about its etiology or clinical significance. To better understand the cause of this phenomenon, we studied 49 patients without renal dysfunction or osteomalacia who underwent parathyroidectomy for primary hyperparathyroidism. Patients were categorized into 2 groups based on their serum PTH and calcium levels after parathyroidectomy: (1) elevated PTH with eucalcemia (n = 21), (2) normal PTH with eucalcemia (n = 28). Elevation of serum PTH with eucalcemia after parathyroidectomy occurred in 43% of patients. Patients in group 1 had significantly higher preoperative and postoperative mean serum PTH levels and significantly lower postoperative serum levels of 1,25(OH)(2)D(3), 1,25(OH)(2)D(3)/25(OH)D(3) ratio, and 1,25(OH)(2)D(3)/PTH ratio compared with patients in group 2. Serum PTH in group 1 patients normalized as early as 3 months, but remained elevated in some patients for more than 4 years, and was not associated with development of recurrent hypercalcemia. Normalization of serum PTH in group 1 patients was associated with significant increase in 1,25(OH)(2)D(3) and 1,25(OH)(2)D(3)/PTH ratio. Our data suggest that elevation of serum PTH in eucalcemic patients after parathyroidectomy is a frequently reversible state of resistance of the kidneys to PTH-mediated 1-alpha hydroxylation of 25(OH)D(3) and does not signify subsequent recurrence of hyperparathyroidism.