Supplementary Material for: Clinical Effectiveness of Calcium Oxalate Stone Treatments

Introduction: Lowering kidney stone risk and urine calcium oxalate supersaturation is a primary clinical focus for kidney stone prevention and can be achieved with multiple strategies. Common strategies include advice to increase fluid intake, restrict dietary sodium, or prescribing a thiazide-type diuretic. We investigated how physicians make these decisions in real-world practice and evaluate their efficacy based on 24-hour urine collections. Methods: We reviewed medical charts for 203 kidney stone formers with idiopathic calcium stones from University of Chicago Kidney Stone Clinic between 2005-2020. Patients had three 24-hour urines before an initial pre-treatment clinic visit and one follow up 24-hour urine. We analyzed changes in urine composition based on treatment advice using t-tests and ANOVA. Results: Patients who received advice to increase fluid intake had lower urine volume at baseline (1.5 vs. 2.5 L/day, p<0.001) and larger increase in urine volume at follow up (0.6 vs. 0.1 L/day, p<0.001) compared to those who did not receive the advice. Patients who were advised to restrict dietary sodium had a higher urine sodium at baseline (208 vs. 139 mEq/day, p<0.001), a larger reduction in urine sodium (-28 vs 13 mEq/day, p=0.002) and larger reduction in urine calcium (-74 vs -28 mg/day, p=0.005) compared with those not advised to restrict dietary sodium. Patients started on a thiazide had a higher baseline urine calcium (281 vs 213 mg/day) and larger reduction in urine calcium (-83 vs -9 mg/day, p<0.001) compared with patients not started on a thiazide. In combination, thiazide prescriptions with dietary sodium restriction reduced urine calcium by 99 mg/day and reduced calcium oxalate supersaturation from 8.0 to 5.5 and calcium phosphate supersaturation from 1.4 to 1.0. Discussion/Conclusion: Providers use 24-hour urine data to guide treatment strategy decisions. These strategies achieved the intended effects on urine composition and lowered kidney stone risk.