Presentation Authors: Stanislav Yuzhakov*, Shavano Steadman, Brandon Otto, Vincent Bird, Benjamin Canales, Gainesville, FL
Introduction: In vitro studies have shown that calcium oxalate supersaturation (CaOX SS) principally drives CaOX stone formation and growth. As this has not been previously validated in humans, the objective of this study was to investigate the link between 24-hour urine CaOX SS and &[Prime]in vivo&[Prime] CT stone growth.
Methods: From a database of 368 patients with >70% CaOX stone composition, we identified 72 individuals who, prior to stone intervention, obtained at least two separate CT scans and at least one 24-hour urine collection between the CT studies. In addition to demographic and laboratory data, two reviewers, blinded to each other&[prime]s findings, calculated bilateral 3D kidney stone volume using an ROI Pen Tool (Visage 7® Platform) on all image series. When measurements differed by >10%, a third reviewer served as an arbitrator. The difference between first and second CT was divided by time between scans, yielding % stone volume growth per year (%/year). CaOX SS were grouped into low ( < 5), medium (5-10), and high risk (>10). Statistical significance between groups was assessed by the Kruskal-Wallis test.
Results: All 72 individuals had stone growth as measured by 3D CT with mean interval between studies of 7 +/- 6 months. Inter-reviewer reliability of CT volume measurement was well correlated at 0.98 (Gwet&[prime]s AC2), and an arbitrator was only needed in 14/144 (10%) cases. Median stone % growth/year was 29%, 77%, and 169% for low, medium, and high risk groups, respectively (p = 0.02; Figure). Despite marked inter-individual stone growth variation, a best fit of mean CaOX SS vs. stone volume growth rate (%/year) showed a positive moderate correlation (Spearman&[prime]s rho = 0.42, p < 0.001).
Conclusions: In our population of calcium oxalate stone formers, increased 24-hour CaOX SS risk was associated with increased stone growth rate. Further investigations using CT volumetric stone growth measurement may allow for noninvasive, &[Prime]in vivo&[Prime] study of stone growth modulators, to improve stone prediction and allow for future stone growth simulators.