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Introduction: Non-obstructing renal stones are a potential cause of recurrent urinary tract infections. However, there is little clinical data to distinguish infected from uninfected renal stones.
Materials & Methods: We performed a retrospective review of patients who underwent unilateral ureteroscopy for non-obstructing renal stones from 9/2008 - 6/2010. Stone culture was routinely sent if a stone was retrieved. Patients were excluded if they had hydronephrosis, ureteral stones, indwelling stent, bilateral procedures, or ipsilateral percutaneous nephrolithotomy or shock-wave lithotripsy in the preceding 12 months. Stone dimensions were independently measured from CT images.
Results: Ureteroscopy was performed in 43 renal units in 41 patients with a mean of 2.3 stones per renal unit. Four (9.3%) renal units had a stone culture with at least one bacteria while 39 (90.7%) had no growth. Stone microbiology included alpha-hemolytic Streptococcus (1 stone), Enterococcus (2 stones), and coagulase-negative Staphylococcus (1 stone). Eight (18.6%) patients had a diagnosis of recurrent UTIs, but only 1 (2.3%) had a stone culture that correlated with at least one prior urine culture. Mean stone size was 7.14 + 3.16 mm x 5.44 + 2.24 mm in the axial plane. There was no statistically significant difference in stone length, width, height, axial ellipsoid area, or ellipsoid volume between patients with and without positive stone cultures.
Conclusions: Non-obstructing renal stones have a low but non-negligible incidence of infection in this patient population. Larger studies are needed to identify predictive variables for stone infection to guide patient selection for surgical intervention.