2305 DOES BIOCHEMICAL RISK PROFILE MATCH STONE COMPOSITION FOR CALCIUM OXALATE, URIC ACID, AND MIXED STONE FORMERS?

Abstract

INTRODUCTION AND OBJECTIVES: Previous studies have demonstrated differences in clinical and biochemical profiles of patients with pure uric acid (UA) and pure calcium oxalate (CaOx) calculi. However, to what degree they differ compared to patients with mixed CaOx/UA calculi is unknown. Therefore, we sought to determine how patients with mixed stone composition compare to the pure stone formers on 24-hour urine analysis. METHODS: We performed a retrospective review of 232 patients with both stone composition analysis and 24 hour urinalysis (Litholink®). Analysis of 24-hour urine constituents across the 3 stone groups (pure UA, pure CaOx and mixed CaOx/UA) was performed using univariable analysis of variance and multivariable linear regression models adjusting for urine volume, creatinine excretion and clinical and demographic factors. RESULTS: A total of 27 (11.6%) patients had mixed CaOx/UA, 122 (52.6%) had pure CaOx and 83 (35.8%) had pure UA calculi. Univariable analysis demonstrated significant differences between mixed CaOx/UA patients and pure CaOx patients for urine pH (mixed 5.63 0.49 vs. pure CaOx 5.93 0.51, p 0.009) and supersaturation (SS) of UA (mixed 1.84 1.09 vs. pure CaOx 1.26 0.93, p 0.01), and a significant difference between mixed CaOx/UA patients and pure UA patients for SS of CaOx (mixed 7.18 4.23 vs. pure UA 4.90 2.96, p 0.005). Multivariable analysis demonstrated that mixed CaOx/UA patients had no significant difference in SS CaOx as compared to pure CaOx patients (difference -0.27, p 0.66), while at the same time had no significant difference in SS UA as compared to pure UA patients (-0.07, p 0.69). Additionally, mixed stone composition patients had significantly lower urinary pH (-0.26, p 0.01) and urinary magnesium (-20.1 mg, p 0.019) than pure CaOx patients; these values were not significantly different that those of pure UA patients. (Table 1). CONCLUSIONS: The biochemical risk profile of patients who form mixed CaOx/UA calculi demonstrated abnormalities that promote both CaOx and UA stone formation. Dietary and medical management for patients with mixed stone composition may require treatment of both defects even if uric acid is the nidus for stone formation in this population.