The improvement of renal concentration capacity after surgery for primary hyperparathyroidism.

Background: Improvement of renal concentration capacity was long ago shown to occur after surgery for primary hyperparathyroidism (pHPT). Study of concentration capacity is of interest, as it was also shown to be a predictive factor for the risk of death in patients with pHPT, and it affected the risk of death independently of 33 other variables in multivariate analysis.

Methods: There were 98 patients with verified pHPT operated on in the years 1958-81, who had urine osmolality determinations performed both before and after surgery: 63 immediately after, and 35 with mean 3.9 years delay (SD = 1.8). Another seven patients with pHPT had urine osmolality determinations performed preoperatively only. Non-parametric sign tests, regression analysis, and correlation tests were performed.

Results: Both patients with severe or moderate, and mild pHPT showed a substantial change of renal concentration capacity, with mean increase of 28.3% (SD = 28.4). The increase generally occurred soon after surgery. In eight out of 98 patients, there was no improvement. A relationship was found between improvement and preoperative peak serum calcium level. In seven out of seven patients followed, untreated for mean 5.3 years (SD = 3.2), there was a mean 15% (SD = 8.0) deterioration of renal concentration capacity.

Conclusions: The findings of this study add cause for surgery in patients with pHPT and give no reason for different treatment of severe, moderate or mild disease.