Differences in metabolic urinary abnormalities in stone forming and nonstone forming patients with primary hyperparathyroidism Mathew D. Sorensen, MD, MS, a Quan-Yang Duh, MD, b Raymon H. Grogan, MD, b Thanh C. Tran, BS, a and Marshall L. Stoller, MD, a San Francisco, CA Background. Hyperparathyroidism 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. Methods. 90 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. Results. Preoperative 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 dif- ferences 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. Conclusion. Metabolic 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. (Surgery 2012;151:477-83.) From the Department of Urology, a and Section of Endocrine Surgery, Department of Surgery, b University of California, San Francisco, CA NEPHROLITHIASIS developed in almost half of the pa- tients with primary hyperparathyroidism (HPTH) before routine testing of serum calcium concentra- tions. 1 Over the last 30 years, however, the incidence of nephrolithiasis has decreased to less than 20% as patients tend to be diagnosed at an earlier and often asymptomatic stage. Primary HPTH is diagnosed in 2–8% of patients with a history of nephrolithiasis. 2 The formation of calcium-based nephrolithiasis among patients with primary HPTH is attributed largely to hypercalciuria. 3,4 Increased serum levels of parathyroid hormone (PTH) increase intestinal absorption, bone resorption, and renal reabsorp- tion of calcium leading to an increase in serum cal- cium concentrations. 5 Despite the increased renal reabsorption of calcium, hypercalciuria results from the excess calcium load. Thus, one would expect to find hypercalciuria in all patients with untreated primary HPTH, placing all patients at in- creased risk of nephrolithiasis. Recent studies have demonstrated that patients with primary HPTH and a history of nephrolithi- asis have no identifiable differences in preopera- tive serum parameters, intestinal absorption of calcium, bone mineral density, or preoperative 24-hour urine levels when compared with those without nephrolithiasis except perhaps a slightly Accepted for publication July 8, 2011. Reprint requests: Mathew D. Sorensen, MD, MS, Department of Urology, University of California, San Francisco, 400 Parnassus Avenue, A610, San Francisco, CA 94143. E-mail: mathews@uw. edu. 0039-6060/$ - see front matter Ó 2012 Mosby, Inc. All rights reserved. doi:10.1016/j.surg.2011.07.039 SURGERY 477