Differences in metabolic urinary abnormalities in stone forming and nonstone forming patients with primary hyperparathyroidism

BackgroundHyperparathyroidism is associated with hypercalciuria and nephrolithiasis. Urine calcium excretion decreases after parathyroidectomy, but whether there is a differential decrease between stone and nonstone formers remains controversial. We evaluated differences between stone formers and non-stone formers in serum and urinary parameters before and after parathyroidectomy.Methods90 patients, 40 with and 50 without a history of nephrolithiasis underwent parathyroidectomy for hyperparathyroidism; 24-hour urine samples were collected before and after parathyroidectomy. Overall, 92% of patients provided samples before parathyroidectomy and 63% after parathyroidectomy. Preoperative, postoperative and changes in urinary parameters were evaluated.ResultsPreoperative hypercalciuria was present in ∼65% in both groups (P = .68). Parathyroidectomy decreased serum levels of calcium, parathyroid hormone, and urinary calcium, but there were no differences between stone formers and nonstone formers. Stone formers were 12-fold (P = .001) more likely to resolve an increase in supersaturation of calcium oxalate (SSCaOx), and after adjustment for age, sex, and BMI were 46-fold (P = .002) more likely to resolve an increase in SSCaOx. After parathyroidectomy, the rate of stone recurrence was 23% and male sex (aOR 20, P = .032) and increasing BMI (aOR 1.23, P = .038) were the only independent predictors of stone recurrence after adjusting for age. No other factor evaluated preoperatively, postoperatively, or the change after parathyroidectomy differentiated stone and nonstone formers or predicted stone recurrence.ConclusionMetabolic evaluation did not differentiate stone formers from nonstone formers reliably. Stone formers were more likely to resolve an increase in SSCaOx after parathyroidectomy. Male sex and increasing BMI were independently associated with stone recurrence after parathyroidectomy.