Presented by: Mark I Sultan MD
University of California, Irvine

Introduction

24-hour urine collections are obtained as part of the metabolic workup for nephrolithiasis to identify modifiable abnormalities for stone prevention. We sought to discern trends in the prevalence of metabolic abnormalities based on body habitus.

Materials

All Litholink 24-hour urine collections for nephrolithiasis patients obtained at our institution between 2004 and 2020 were retrospectively reviewed. Only the first 24-hour urine collection prior to therapy for each patient was included the analysis. Patients were classified according to Body Mass Index (BMI) as underweight (<18.5), normal (18.5 - 25), overweight (25-30), and obese (>30). Litholink’s gender specific reference ranges were used to define abnormalities. 

Results

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1372 patients were included. The mean age was 56 ± 15.3 (53.5% male, 46.5% female). Overall, the most common metabolic abnormality was elevated urine sodium (52.8%), while the least common was a low urine pH (15.6 %). Table 1a reports the prevalence of metabolic abnormalities among the groups, table 1b reports the median value and significance of variation between the groups. On subgroup analysis, obese stone formers compared to normal patients were more likely to have hypercalciuria OR=1.36 [1.036-1.794], hyperoxaluria OR=1.85 [1.40-2.45], elevated urine sodium OR=2.60 [1.98-3.41], hyperuricosuria OR=3.09 [2.22-4.31], low urine pH OR=3.86 [2.60-5.75], and high uric acid supersaturation OR=3.20 [2.37-4.34]. 

Conclusion

Body weight differences are associated with different risk profiles on a 24 hour urine collection. Obese patients are more likely to harbor metabolic derangements on a 24-hour urine analysis compared to normal patients. These findings highlight the importance of lifestyle and dietary modifications to correct obesity in addition to directed medical therapy for stone formers.

Funding

None

Lead Authors

Mark I Sultan, MD
University of California, Irvine

Co-Authors

Pengbo Jiang, MD
University of California, Irvine

Sohrab N Ali, MD FRCSC
University of California, Irvine

Roshan M Patel, MD
University of California, Irvine

Ramy Youssef, MD
University of California, Irvine