Residual Urinary Volume and Urinary Tract Infection—When are They Linked?

PURPOSE: Large post-void residual urinary volume may be related to the development of urinary tract infection. However, the maximum post-void residual volume that predisposes patients to a higher risk of urinary tract infection is not known. In this prospective study we determined the cutoff value for post-void residual volume that places adult men at risk for bacteriuria. MATERIALS AND METHODS: Data were obtained from 196 consecutive healthy adult men (median age 62 years) who came for prostate evaluation without symptoms of acute urinary tract infection. Right after spontaneous voiding, bladder catheterization was performed under normal aseptic conditions, and the post-void residual volume measured. Urine samples were collected for culture from each patient and the results were compared to the various post-void residual volume. RESULTS: Overall 27% of the patients presented with a positive urine culture. The mean post-void residual volume in this group was 257 ml (range 150 to 560) compared to 133 ml (range 10 to 340) for the group with negative culture (p <0.001). The post-void residual volume value of 180 ml was determined to have the best specificity and sensitivity. The positive predictive value for bacterial growth at a post-void residual volume of 180 ml or greater was 87.0% and the negative predictive value was 94.7%. CONCLUSIONS: Clinically asymptomatic adult men with a post-void residual volume of 180 ml are at a high risk for bacteriuria. Such cases require close medical attention since it may be necessary to introduce early drug therapy or surgical intervention to improve the bladder emptying.