Investigating Fluid Intake in an Underserved Community: What Factors Are Associated with Low Urine Volume on 24-Hour Urine Collection?

Background: Stone prevention is dependent on high fluid intake, with evidence that low urine volume (LUV) can promote nephrolithiasis in the absence of other metabolic abnormalities. Herein, we investigate patient-related factors associated with LUV on initial 24-hour urine collection in an underserved population. Materials and Methods: A retrospective chart review was performed of patients treated by a single surgeon for nephrolithiasis from August 2014 to January 2019. Patients who submitted 24-hour urine samples were divided into two groups based on whether their initial collection was >2 L or not. Factors associated with 24-hour urine volume were analyzed using bivariate and multivariate analyses. As a secondary outcome, we investigated factors associated with corrected 24-hour urine volume on repeat 24-hour urine collection. Results: Two hundred eight patients (45.1%) submitted 24-hour urine collections, 63.9% (133/208) of which demonstrated a urine volume of <2 L. LUV was more common in female patients (77.1% vs 49.5%; p = 0.001) and patients with no insurance and Medicaid (no insurance [100%] vs Medicaid [74.1%] vs Medicare/private [58.6%]; p = 0.02). Female gender and insurance status were independent predictors of LUV in the multivariable analysis. Seventeen of 43 patients (39.5%) with LUV who provided a subsequent collection were able to correct their urine volume. Patients who improved their LUV were older (58.5 vs 45.9 years, p = 0.0149) and more likely to have surgical intervention for their kidney stones (94.1% vs 53.8%, p = 0.006). In our multivariable analysis, surgical intervention was associated with correcting urine volume. Conclusions: Female patients and those with no insurance or Medicaid were more likely to have LUV on an initial 24-hour urine collection. Further research into barriers to fluid intake is important for these two groups, along with directed patient education on strategies for increasing fluid intake.