Friedlander JI, et al. - The aim of this study was to explore the association between urinary cystine parameters and clinical stone activity. The obtained data demonstrates that the target for capacity should be lower than previously advised.

Methods

• In this study, researchers prospectively followed 48 cystinuric patients with 24-hour urine collections and serial imaging studies and recorded stone activity.
• Cystine urinary parameters at times of stone activity were compared with those obtained during periods of stone quiescence and then performed correlation and ROC analysis to evaluate the performance of cystine parameters in predicting stone activity.

Results

• Over a median follow-up of 70.6 months (range 2.2 to 274.6 mo.), 85 stone events occurred that could be linked to a recent urine collection.
• The data indicated that cystine capacity was significantly greater for quiescent urines than stone event urines (48 ± 107 mg/L vs. -38 ± 163 mg/L, p<0.001, respectively).
• Evidence showed that cystine capacity was significantly inversely correlated with stone activity (r = -0.29, p<0.001).
• They noted that capacity was also highly negatively associated with both supersaturation (r = -0.88, p<0.001) and concentration (r = -0.87, p<0.001).
• Applying the suggested cutoff of >150 mg/L has a sensitivity of only 8.0% for predicting stone quiescence.
• Decreasing the cutoff to ≥90 enhanced sensitivity (25.2%) while maintaining specificity (90.9%).