Presented by: Orel Carmona MD
Sheba Medical Center

Introduction

Urine metabolic abnormalities are considered the etiology of nephrolithiasis, and as so it is recommended in both the EAU and AUA guidelines to perform a metabolic evaluation for recurrent stones formers. However, certain patients present with recurrent unilateral renal stones, while the mate kidney consistently remains stone free.  The purpose of this study was to explore whether metabolite differences between urine samples of mate kidneys can explain lifetime unilateral renal stone formation.

Materials

We retrospectively reviewed our registry database of nephrolithiasis return patients in an attempt to compare 24-hour urine compositions obtained under regular diet and daily activities. Three groups of stone formers were detected: Bilateral stone formers (BSF) and unilateral formers (USF)  whereby 24-hour urine collection reflected two mate kidneys, and past-USF (PUSF) whereby the stone-forming kidney has been resected or declared as non-functioning per renal scan. In the latter group, the urine collection reflected the stone-free kidney.

Results

,

There were 618 patients in the BSF group, 22 in the USF group, and 8 in the PUSF group. The total median follow-up length was 83 months. In the USF group there were higher citrate levels compared to the BSF group (669 mg/24hr vs. 486 mg/24hr, p=0.03), however in the USF group there were unexpectedly higher levels of calcium, uric acid, and oxalate (269 mg/24hr vs 184 mg/24hr p=0.03; 623 mg/24hr vs. 597 mg/24hr p=0.03; 36 mg/24hr vs. 32 mg/24hr p=0.04, respectively).

A sort of "correction" was seen in the PUSF group, whereby normal levels of calcium, uric acid, and oxalate levels were detected (123 mg/24hr; 446 mg/24hr; 24 mg/24hr, p<0.05), yet lower-than-expected levels of citrate were seen (218 mg/24hr, p<0.05). Sodium level was highest in the BSF group and lowest in the PUSF group, however without statistical significance (170 mg/24hr, 158 mg/24hr, 142 mg/24hr, respectively p=0.6).

Conclusion

24-hour urine composition differences between mate kidneys may not serve as a single etiology for lifetime unilateral-renal stone formation. The solution for this enigma may lie at the molecular/genetic level.

Funding

None.

Co-Authors

Miki Haifler, MD
Sheba medical center

Asaf Shvero, MD
Sheba Medical Center

Nir Kleinmann, MD
Sheba Medical Center

Dorit E. Zilberman, MD
Sheba Medical Center