Does 24-Hour Urine Supersaturation Predict Stone Composition?

Background: The aim of the study was to evaluate the correlation between 24-hour urine supersaturation (SS) levels and the crystalline stone composition. Methods: We retrospectively reviewed the results of stone analysis of 386 patients who had completed 24-hour urine stone risk profiles within 2 months of stone analysis. Patients were characterized as calcium oxalate (CAOX), calcium phosphate (CAPH) or uric acid (UA) stone formers based on the predominant component (> 60%) of their stone. Patients with < 50% of one stone composition were characterized as a mixed stone former. Sensitivity, specificity and accuracy of the 24-hour urine SS for predicting the corresponding stone component were calculated. Results: The distribution of stone compositions was 235 (61%) CAOX, 98 (25%) CAPH, 35 (9%) UA and 18 (5%) mixed stone group. At predominant stone mineral concentration ? 60%, the accuracy of 24-hour urine SS for predicting the predominant stone composition was 52.5% for CAOX, 70% for CAPH and 67% for UA group. Even when the predominant stone mineral concentration was ? 90%, the accuracy of SS did not improve: COAX (49%, P = 0.6641), CAPH (77%, P = 0.361) and UA (67%, P = 0.9593). Conclusions: Twenty-four-hour urine SS has a poor accuracy to predict the predominant stone composition. Accuracy is highest for patients with CAPH stones. World J Nephrol Urol. 2015;4(1):169-172 doi: http://dx.doi.org/10.14740/wjnu206w