Midstream urine culture and sensitivity test is a poor predictor of infected urine proximal to the obstructing ureteral stone or infected stones: a prospective clinical study.

Purpose: This prospective study was performed to determine if midstream urine (MSU) culture and sensitivity (C&S) alone could adequately predict infected urine proximal to the obstructing ureteral stone or the infected stones. Can pelvic urine C&S predict infected stones?
Materials and Methods: A prospective clinical study was performed on all patients undergoing ureterorenoscopy and lithotripsy for ureteral stones with obstruction between December 1, 2000 and January 31, 2002. We obtained MSU, renal pelvic urine and fragmented stones for culture and sensitivity. An analysis of the data was performed to assess statistical association.
Results: A total of 73 patients who fulfilled the criteria were recruited. Of these patients 25 (34.3%) had positive stone culture, 43 (58.9%) had positive pelvic urine and 21 (28.8%) patients had positive MSU C&S. Stone and pelvic C&S were positive simultaneously in 17 (23.3%) cases, MSU and stone C&S were positive in 8 (10.9%) cases, whereas pelvic and MSU C&S were positive in 13 (16.4%) cases (p = 0.03). MSU C&S had a sensitivity of 30.2% and specificity of 73% to detect pelvic urine C&S positivity. MSU C&S had a low positive predictive value and negative predictive value (NPV) in relation to infected pelvic urine (positive predictive value = 0.62, NPV = 0.42). Pelvic urine C&S had a NPV of 0.73 in detecting noninfected stones.
Conclusions: The results of this study suggest that in obstructive uropathy secondary to a stone MSU C&S is a poor predictor of infected urine proximal to the obstruction and infected stones.