Presented by: Sagi A. Shpitzer MD
Rabin Medical Center

Introduction

Introduction: Ammonium urate (AU) crystals are a rare component of urinary stones. In general AU appears primarily in mixed composition stones while pure AU stones are rare. The clinical significance of AU is unclear. In this study we sought to investigate the clinical as well as the metabolic characteristics of patients with an AU stone component.

Materials

Methods: A large healthcare database was searched for adult patients with laboratory results of a stone composition analysis between the years 2013-2020. A stone was considered as having an AU component if it consisted on analysis of >10% AU. AU stone formers were subdivided according to the additional predominant stone component. Results were compared to patients with similar predominant stone compositions without an AU component.

Results

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Results: Out of 11,979 patients with a stone composition analysis in our database 141 stones (1.2%) were classified as AU stones. None of the stones were pure ammonium urate. Patients were divided into uric acid (UA, n=51), calcium oxalate (CaOX, n=56) and infection stone (IS, n=34) subgroups. The UA group had a higher proportion of female patients (47% vs. 25%, p<0.001) and of patients with inflammatory bowel disease (IBD) (5.9% vs. 1.8%, p=0.045). The CaOX group had similar findings with 45% females vs. 22% (p<0.001) and 8.9% IBD patients vs. 2.4% (p<0.001). The IS group had more patients from low socioeconomic groups (39% vs. 14%, p<0.001) but no difference regarding gender (47% vs. 58% female, p=0.19). When comparing the results of metabolic evaluation differences were found only in the UA group which had a higher prevalence of hyperoxaluria (41.2% vs. 17.1%, p<0.001) and a trend towards hypocitraturia (50% vs. 33%, p=0.09). Average spot urine pH was acidic in all 3 subgroups - 5.67, 5.86 and 6.3 in the UA, CaOX and IS groups respectively.

Conclusion

Conclusions: Patients with AU containing stones are more likely to be women and to suffer from IBD, but in most other respects are similar to patients with matching stone composition without an AU component. It is unclear whether patients with AU containing stones should be treated any differently than patients without AU stones.

Funding

None

Co-Authors

Yaron Ehrlich, MD
Rabin Medical Center

Abd E. Darawsha, MD
Rabin Medical Center

David Lifshitz, MD
Rabin Medical Center