Post-void residual urine as a predictor of urinary tract infection--is there a cutoff value in asymptomatic men?

Post-void residual urine can lead to various complications, including urinary tract infection. Recently investigators calculated that a cutoff value of 180 ml has considerably high sensitivity and specificity for significant bacteriuria in asymptomatic men. We determined the association between post-void residual urine volume and urinary tract infection, and validated the suggested 180 ml cutoff in asymptomatic men.

In a prospective study we analyzed certain criteria in 225 asymptomatic male patients, including prostate specific antigen, prostate volume, International Prostate Symptom Score, peak urine flow rate, urine culture results and post-void residual urine volume using transabdominal ultrasound. Using ROC analysis a cutoff predicting bacteriuria was calculated. Different cutoff values were validated.

Of the study group 60% were able to completely empty the bladder and had a post-void residual urine volume of 10 ml or less. However, in 31% of the study group urine culture was positive. Patients presenting with urinary tract infection had significantly higher mean post-void residual urine volume than patients without urinary tract infection (113 vs 41 ml, p <0.001). In 29 men (13%) post-void residual volume was 180 ml or greater. Confirming urinary tract infection, this cutoff showed only 28% sensitivity and 94% specificity (AUC 0.606, p = 0.01).

No cutoff value could be determined to predict positive urine culture with sufficient sensitivity and specificity. Based on the results of the current study it seems premature to recommend a cutoff value leading to therapeutic consequences.