Do Urinary Cystine Parameters Predict Clinical Stone Activity?
We prospectively followed 48 patients with cystinuria using 24-hour urine collections and serial imaging, and recorded stone activity. We compared cystine urinary parameters at times of stone activity with those obtained during periods of stone quiescence. We then performed correlation and ROC analysis to evaluate the performance of cystine parameters to predict stone activity.
During a median follow-up of 70.6 months (range 2.2 to 274.6), 85 stone events occurred which could be linked to a recent urine collection. Cystine capacity was significantly greater for quiescent urine than for stone event urine (mean SD 48 107 vs e38 163 mg/l, p <0.001). Cystine capacity significantly correlated inversely with stone activity (r 1⁄4 e0.29, p <0.001). Capacity also correlated highly negatively with supersaturation (r 1⁄4 e0.88, p <0.001) and concentration (r 1⁄4 e0.87, p <0.001). Using the suggested cutoff of greater than 150 mg/l had only 8.0% sensitivity to predict stone quiescence. Decreasing the cutoff to 90 mg/l or greater improved sensitivity to 25.2% while maintaining specificity at 90.9%.
Our results suggest that the target for capacity should be lower than previously advised.
Authors:
Justin I. Friedlander, Jodi A. Antonelli, Noah E. Canvasser, Monica S. C. Morgan, Daniel Mollengarden, Sara Best and Margaret S. Pearle
From the Department of Urology, University of Texas Southwestern Medical Center (JIF, JAA, NEC, MSCM, DM) and Jane and Charles Pak Center for Mineral Metabolism and Clinical Research, Dallas (MSP), Texas, and Department of Urology, University of Wisconsin (SB), Madison, Wisconsin
J Urol. 2018 Feb;199(2):495-499. doi: 10.1016/j.juro.2017.09.034. Epub 2017 Sep 12.