Comparison of metabolic parameters between pure-uric acid and mixed-uric acid kidney stone formers

We seek to compare clinical and 24-h urine parameters between pure-uric acid (UA) and UA–CaOx stone formers in our practice and explore how any differences in metabolic profiles could suggest different prevention strategies between the two groups.

We retrospectively reviewed patients with either pure- or mixed-UA nephrolithiasis from 2020 to 2023 at a tertiary care center. We included patients with a 24-h urine collection and a stone analysis detecting any amount of UA. Patients were organized into two cohorts: (1) those with 100% UA stones and (2) < 100% UA stones. Differences in demographic characteristics were compared between pure-UA and UA–CaOx stone formers. Twenty-four hour urine metabolic parameters as well as metabolic abnormalities were compared between the pure-uric acid and mixed-uric acid groups.

We identified 33 pure-UA patients and 33 mixed-UA patients. Patient demographics were similar between the groups (Table 1). Pure- and mixed-UA patients had a similar incidence of metabolic syndrome, diabetes, history of stones, and stone burden.

We found the pure-UA cohort to have 24-h lower urine volume (1.53 vs. 1.96 L/day, p = 0.045) and citrate levels (286 vs. 457 mg/day, p = 0.036). UA–CaOx stone formers had higher urinary calcium levels (144 vs. 68 mg/day, p = 0.003), higher urinary oxalate levels (38 vs. 30 mg/day, p = 0.017), and higher median urinary calcium oxalate super-saturation (3.97 vs. 3.06, p = 0.047).

Pure-UA kidney stone formers have different urinary metabolic parameters when compared with UA–CaOx stone formers, thus requiring different and tailored medical management.