Presented by: Sagi A. Shpitzer MD
Rabin Medical Center

Introduction

Introduction: Uric acid (UA) stone formers are commonly defined as patients with a predominant (>50%) UA component. However when considering stone dissolution, it is important to differentiate between pure and mixed UA stone formers. In this study we sought to investigate the differences between these two populations in a large cohort of surgically treated nephrolithiasis patients.

Materials

Methods: A large healthcare database was searched for adult patients with laboratory results of a stone analysis between the years 2013-2020. Pure and mixed UA stones were defined as stones containing ≥95% and >50% UA respectively. Demographic, clinical, and laboratory results were compared between the groups.

Results

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Results: Out of 11,979 patients with a stone composition analysis in our database 1,366 stones (11.4%) were classified as UA stones of which 904 were pure and 462 were mixed. The male-to-female ratio was 3:1 in both groups. Pure UA stone formers were older (63.8 vs. 61.1 years, p<0.01) and more likely to be of Jewish ethnicity (82% vs. 76.6%, p<0.01). Comorbidities including diabetes, ischemic heart disease, hypertension and chronic kidney disease were significantly more frequent in the pure UA group, with the highest difference observed in the diagnosis of diabetes (62.7% vs. 51.5%, p<0.01). No significant difference in BMI was found between the groups (30.56 vs. 30.93, p=0.267). Blood uric acid levels were slightly higher in the pure UA group (6.56 vs. 6.38 mg/dL, p=0.04) while urinary uric acid levels as well as calcium and citrate did not differ. Urinary pH in the pure group was slightly higher (5.53 vs. 5.47, p=0.03).

Conclusion

Conclusions: Mixed and pure uric acid stone formers differ in certain demographic and clinical aspects. Older patients with diabetes are more likely to present with pure UA stones. Urine pH and 24-hour urine collection do not allow differentiation between the groups.

Funding

None

Co-Authors

Hadar Tamir, MD
Rabin Medical Center

Yaron Ehrlich, MD
Rabin Medical Center

Abd E. Darawsha, MD
Rabin Medical Center

David Lifshitz, MD
Rabin Medical Center