It is well known that urinary calculi are associated with urinary tract infections. Post-operative sepsis is one of the major complications after various endourological procedures for stone surgeries. These episodes of sepsis occur even in negative urine cultures. Stones have been found to harbour bacteria which on fragmentation causes bacteremia and sepsis. Thus, usual practice of pre-operative urine culture cannot truly predict the occurrence of post-operative sepsis. It also seems logical that intra-operative stone cultures could guide us for early management of such episodes of sepsis. The purpose of this study was to determine if there exists any association between urine and stone cultures in patients undergoing endourological stone surgeries.
This is a prospective comparative observational study, in patients undergoing endoscopic procedures for calculus in urinary tract. Mid-stream urine cultures were obtained 3 to 5 days prior to surgery and crushed stone culture during the surgery. Comparison was then made between the two with respect to positivity, location of calculus and bacterial flora.
A total of 122 cases of urolithiasis were included, in which 30 (24.59%) cases had a positive urine culture, whereas 62 (50.82%) patients were positive for stone culture. This significant difference was maintained only in renal stones on subset analysis (p value < 0.0001). Both cultures were positive in only 15% of cases, and bacteriological analysis showed same organism in just 6.5% of cases. In our study, sensitivity, specificity, positive predictive value, negative predictive value and diagnostic accuracy of urine culture against the stone culture were 29.03%, 80%, 60%, 52.17% and 54.09%.
The results of our study suggests that pre-operative urine cultures have a poor predictive value and accuracy for infective organism in the renal stone. Therefore, stone culture should be included in routine protocols during renal endourologic surgery for stones.