Investigating 24-Hour Urine Expected Ranges of Non-Kidney Stone Formers: an EAU Endourology Research Group Systematic Review and Meta-Analysis

Background and Objective: There is substantial variation in reference ranges for 24-hour urine collections, leading to diagnostic uncertainty. We aimed to curate robust evidence for expected ranges of 24-hour urine collections in the non-kidney stone forming population. Methods: We performed a systematic review (PROSPERO ID: CRD42024590784) of healthy adults without kidney stone disease undergoing 24-hour urine collections. Each component was meta-analysed in R, stratified by age, sex and ancestry, meta-regression and sensitivity analyses for study design, collection completeness and bias. An explicit eight-branch decision framework selected the recommended analysis per component. Expected ranges were derived from the pooled SD (95% interval); evidence was quantified by GRADE. Key Findings and Limitations: Seventy-two articles were included (10,284 participants). Expected ranges (mmol / 24 h unless stated): volume 1.0-2.5L, calcium 1.9-6.2, oxalate 0.2-0.6 (men) / 0.2-0.4 (women), urate 2.0-5.1(men)/2.3-3.5(women), pH 5.6-6.3, citrate 1.2-4.5, creatinine 12.2-16.3(men)/7.2-12.6(women), phosphate 19-26, sodium 98-253, potassium 28-77, magnesium 3.1-4.8, ammonium 28-46(men)/20-40(women), chloride 84-218, sulphate 17-26(men)/7-30(women), urea 234-445. Principal limitations were: high between-study heterogeneity (I-squared>95% for most components) and assay/laboratory variability (most marked for citrate and potassium). Conclusions and Clinical Implications: This is the first study to attempt a robust characterization of 24-hour urine expected ranges using meta-analysis. Six of the derived expected ranges (pH, oxalate, magnesium, sulphate, urate, creatinine) were broadly concordant with existing reference ranges, providing an evidence base for those specific components.