Optimizing Screening Performance for the Risk of Hyperoxaluria and Urolithiasis Using the Urinary Oxalate/Creatinine Ratio: A Retrospective Analysis.

Background and objective: The risk of chronic kidney disease (CKD) and nephrolithiasis increases with higher levels of oxalate excretion in 24-h urine, warranting monitoring in specific populations, especially after malabsorptive bariatric surgery. However, implementation of systematic 24-h urine collection is challenging, so there is a need for alternative screening methods. Methods: Using retrospective data from patients evaluated for the risk of urolithiasis, we assessed different thresholds for the urinary oxalate/creatinine (UOx/Creat) ratio to optimize the screening performance for hyperoxaluria diagnosis and urolithiasis risk using lithogenic risk surrogates. Key findings and limitations: Among 1264 patients referred for urolithiasis, 38% were excluded because urine collection was considered incomplete. The remaining 786 individuals were included in our analysis, of whom 16% exhibited hyperoxaluria. A UOx/Creat screening threshold between 35 and 45 μmol/mmol demonstrated good performance, depending on the clinical weighting for false-negative versus true-positive results and the cost/benefit ratio. Conclusions and clinical implications: The UOx/Creat ratio is a promising tool in screening for hyperoxaluria-related complications. However, future research is needed to validate its performance and address the limitations identified to confirm its clinical relevance and effectiveness. Patient summary: Our study shows that a simple test to measure the ratio of oxalate to creatinine in urine can help in identifying people at risk of kidney stones, especially for patients who have had weight-loss surgery. The test showed good screening performance, but more research is needed to confirm our findings.