Quantification of asymptomatic kidney stone burden by computed tomography for predicting future symptomatic stone events

Objective To find the optimal characterization of asymptomatic radiographic stone burden on computed tomography (CT) scans. Methods A survey was sent to stone formers who underwent a CT scan while asymptomatic during a stone clinic evaluation. Symptomatic stone passage events after CT scan were detected by survey and medical record review. Radiographic stone burden was quantified by number of stones, largest stone diameter, automated total stone volume (TSV), and bilateral stones and then compared as predictors of stone events. Results There were 550 stone formers; 43% had a stone event for a median of 4.7 years after the CT scan. Stone burden by quartiles was 0-1, 2-3, 4-6, and ≥7 for number of stones; 0-2, 3-4, 5-7, and ≥8 mm for largest stone diameter; and 0-8, 9-78, 79-280, and ≥281 mm 3 for TSV; 48% had bilateral stones. The hazard ratios (HRs) for symptomatic event was 1.30 ( P P P P P  = .01). This risk of events with TSV was also independent of demographics, urine chemistries, and stone composition. Among the 53 patients with interim events between CT scans, a rapid increase in TSV between CT scans (>570 mm 3 per year) predicted subsequent events (HR, 2.8; P  = .05). Conclusion Automated TSV is more predictive of symptomatic events than manual methods for quantifying stone burden on CT scan.