Comprehensive Nomogram for Prediction of the Uric Acid Composition of Ureteral Stones as a Part of Tailored Stone Therapy

Abstract

Background: Oral chemolitholysis is a noninvasive therapy for uric acid (UA) stones. Proper patient selection is crucial for success of the therapy. Objective: To develop a nomogram for prediction of UA stones using parameters gathered during emergency work-up for flank pain. Design, setting, and participants: A single-center cohort (459 patients) with singular ureteral stones and available stone analysis was retrospectively reviewed for radiological, urinary, and serological findings indicating UA stones. Outcome measurements and statistical analysis: A Mann-Whitney U test or Kruskal-Wallis test was applied for univariate analysis. Categorical variables were compared using a χ2 test. Binary logistic regression of significant parameters was performed to design the nomogram. Results and limitations: Univariate analysis revealed statistically significant differences in parameters between predominantly UA and non-UA groups, including median age (60 yr, interquartile range [IQR] 51.5–70.5 vs 51 yr, IQR 39–62; p < 0.001), body mass index (30.0 kg/m2, IQR 27.25–35.0 vs 26.6 kg/m2, IQR 24.0–30.467; p < 0.001), stone density (435.0 HU, IQR 329.0–528.0 vs 750.0 HU, IQR 548.0–995.0; p < 0.001), serum UA (437.5 μmol/l, IQR 374.25–478.0 vs 321.0 μmol/l, IQR 273.0–377.0; p < 0.001), and urine pH (5.5, IQR 5.0–5.5 vs 6.0, IQR 5.5–6.5; p < 0.001). Radiolucency was more frequent in the predominantly UA group (88.60% vs 32.70%; p < 0.001). Multivariate binary logistic regression confirmed age, body mass index, stone density, serum UA, urine pH, and radiolucency as independent predictors of UA stones and these parameters were used to design the nomogram. Conclusions: We present a nomogram for the prediction of uric acid stones. Patient summary: We developed a nomogram as a simple tool with potential to be useful in patient counseling regarding chemolitholysis as a tailored stone treatment for uric acid urinary stones.