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TAIPEI, TAIWAN (UroToday.com) - Introduction and Objectives: The goal of treatment for cystinuria has historically been to achieve a cystine concentration below the solubility limit (250 mg/L). Other estimates of cystine stone-forming potential include cystine supersaturation and cystine capacity, a proprietary assay from the commercial laboratory, Litholink® (Chicago, IL). The superiority of one measure of stone- forming potential over the others has not yet been determined. We sought to compare the ability of urinary cystine parameters in predicting clinical stone activity.

wceMethods: We prospectively followed 35 well-characterized cystinuric patients and recorded stone activity, defined as an increase in size of existing stones, development of new stones, and passage or intervention for stones not previously seen on imaging. We compared capacity, concentration, and supersaturation obtained at times of stone activity with those obtained during periods of quiescence and then performed ROC analysis to evaluate the performance of the tests in predicting clinical stone activity.

Results: With mean follow-up of 61.7 months (range 4.7– 262.9 months), 63 stone events occurred that could be linked to a recent urine collection, while 183 urines were submitted during periods of quiescence. Statistical analysis demonstrated significant differences between stone event and quiescent urine collections for mean cystine supersaturation 1.08 vs. 0.82, mean cystine concentration 321.8 mg/l vs. 235.6 mg/l, and mean cystine capacity - 22.8 vs. 62.3, respectively (all p < 0.01). ROC analysis revealed an AUC of 0.74 for supersaturation, 0.71 for concentration, and 0.74 for capacity (p > 0.05).

Conclusions: Urinary cystine parameters correlate with clinical stone activity; however, no parameter demonstrated superiority with regard to differentiating stone activity from inactivity.

Source of Funding: None

View an interview with Justin Friedlander, one of the authors of this study.


Presented by Justin Friedlander,1, 2 Jodi Antonelli,2 Monica Morgan,2 Daniel Mollengarten,2 Sara Best,3 and Margaret Pearle2 at the 32nd World Congress of Endourology & SWL - September 3 - 7, 2014 - Taipei, Taiwan

1Einstein Healthcare Network, Urologic Institute of Southeastern Pennsylvania, USA
2University of Texas Southwestern Medical Center, USA
3University of Wisconsin, USA


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