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Introduction

The influence of obesity on the effectiveness of KCit to reduce calcium stone risk is not well-characterized. We evaluated 24h urinary risk factors in both obese (BMI ≥ 30) and non-obese stone formers (SFs) and compared treatment-associated changes after starting KCit. As there is a concern for forming calcium phosphate (Ca Phos) stones while taking KCit, brushite relative saturation (RS) and pH changes were also assessed.

Methods

With IRB approval, we identified 78 known mixed-calcium SFs from an institutional database (n=78; M:F 34:44; age, 54±15 y; BMI, 31±9). Patients were included in this retrospective analysis if they had stone comprised of >50% calcium and 24-hr urine assays within 3 years before and after initiating KCit, and if BMI at the time of collection was documented. RS indices were calculated with Equil2. Patients were divided into non-obese stone formers (NOSF, BMI<30) and obese stone formers (OSF, BMI ≥ 30). Pre- and post-KCit 24-h urinary parameters were examined using univariate and multivariate analyses with BMI as a covariate. To control for multiple statistical comparisons, the Bonferroni correction revealed that a p value <0.003125 was required for significance.

Results

Baseline 24-h urine values were similar in both groups, though OSF had a higher uric acid RS (1.45 vs 0.60, p=0.002), likely due to more acidic urine (pH 5.8 vs 6.3, p=0.009). Significant increases in urine potassium in both groups suggested KCit compliance (NOSF: +13, p=0.001; OSF: +28, p<0.0001). Both NOSF and OSF had statistically significant increases in urine citrate (233 to 286, p=0.003; 289 to 575, p<0.0001) and pH (6.3 to 6.6, p=0.001; 5.8 to 6.5, p<0.0001). Post therapy brushite RS was similar in NOSF and OSF (1.85 vs 1.53, p=0.894) and did not exceed the risk cutoff of 2.0. BMI correlated directly with changes in urine calcium and citrate in OSF but not NOSF (-5 vs +17 mg/day, p=0.003; and +63 vs +273, p=0.001, respectively). Changes in urine pH and brushite RS were similar between groups.

Conclusions

Both obese and non-obese calcium SFs experienced favorable changes in urine pH and citrate excretion. However, obese patients were more likely to achieve normocitraturia. Neither group had significant changes in brushite RS while using KCit, perhaps alleviating concerns of CaPhos risk.

Funding

None