Specific urinary characteristics may give rise to each type of pure urinary stone, Ethan Brinkman, BS, of Indiana University School of Medicine, and colleagues revealed during the American Urological Association 2020 virtual experience.

An analysis of 24-hour urine collection data found that patients with 100% pure calcium oxalate dihydrate, apatite, and brushite stones are hypercalciuric (calcium to creatinine ratio greater than 140 mg/g) and have urinary pH higher than 6.0. Calcium oxalate monohydrate stone formers have a neutral pH of 6.0 and hyperoxaluria (45 g/d). Uric acid stone formers do not exhibit hyperuricosuria (0.66 g/d) but nonetheless have uric acid supersaturation of 1.72 together with aciduria (pH less than 5.8), and excess sodium excretion (208 mEq/d).

For the analyses, the investigators employed Beck Analytical Laboratories’ database to identify 123 patients with calcium oxalate monohydrate stones and 70, 88, 174, and 110 patients with calcium oxalate dihydrate, brushite, apatite, and uric acid stones, respectively. Patients with stones of mixed composition or current medical therapy were excluded from the study.

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According to Brinkman’s team, these study findings suggest that not all pure stones are alike, and that unique metabolic derangements create specific urinary environments that may lead to each stone type. Clinicians may be able to use this information to guide management of pure stone formers and conceivably prevent recurrences.

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Brinkman E, Large T, Nottingham C, et al. Metabolic correlates of pure stone subtypes. Presented at the American Urological Association 2020 Virtual Experience, May 15-19, 2020. Abstract MP10-06.