Stone culture in patients undergoing percutaneous nephrolithotomy: a practical point of view.

INTRODUCTION: To determine the clinical yield of stone culture in patients undergoing percutaneous nephrolithotomy (PCNL), and to identify patients who may benefit from this test.

MATERIALS AND METHODS: We queried our database for all patients who underwent PCNL from 2005 to 2017, from whom urine culture (UC) and stone culture (SC) were obtained. Study endpoint was systemic inflammatory response syndrome (SIRS) within 48 hours of PCNL. Risk factors for SIRS and for stone colonization with highly resistant pathogens were evaluated. Based on UC and SC results, we determined the proportion of patients in whom SC may alter the treatment, had SIRS occurred, with respect to the initial empiric treatment.

RESULTS: The study group comprised of 512 patients with a median age of 53, of whom 323 (63%) were male. Positive UC were found in 137 (26.7%) patients, and positive SC in 117 (22.8%) patients. UC did not identify pathogens isolated from SC in 66 (12.8%) patients. Postoperative SIRS occurred in 50 (9.8%) patients. On multivariate analysis only SC was associated with postoperative SIRS. SC pathogens resistance rates ranged from 67% for treatment with 2nd generation cephalosporins to 9% for treatment with meropenem, and may alter the choice of antibiotics in 73 to 12 patients (14.2%-2.3% of the whole cohort), respectively.

CONCLUSIONS: In similar and earlier studies, we found substantial discordance between SC and UC results, and an association between stone colonization and SIRS. However, the practical yield of this test varies with the type of antibiotic given, and is limited when broad spectrum antibiotic is used.