Importance of prostate volume and urinary flow rate in prediction of bladder outlet obstruction in men with symptomatic benign prostatic hyperplasia

OBJECTIVES To predict bladder outlet obstruction with parameters of non-invasive investigations for patients with symptomatic benign prostatic hyperplasia. PATIENTS AND METHODS A sample of 122 men with moderate to severe lower urinary tract symptoms suggestive of benign prostatic hyperplasia was selected. Transrectal prostate ultrasound, free flow measurement, and transabdominal ultrasound for residual urine were carried out together with digital rectal examination for all patients. All patients underwent urodynamic pressure/flow test. Two groups of obstructed (91 patient) and equivocal/unobstructed (31 patient) were analyzed. Probabilistic model based on logistic regression was developed for prediction of obstruction. RESULTS Various parameters were compared in obstructed and non-obstructed/equivocal groups, highlighting important parameters for obstruction. Correlation analysis indicates higher obstruction dependence on average and peak flow rates and lower dependence on total prostate and transition zone volumes, transition zone index. Binary logistic regression model suggests that average flow rate combined with total prostate volume is the best predictor of obstruction (83% of correct predictions; PPV = 92%; NPV = 52%) in the analyzed sample. The analyzed model suggests that peak flow rate could also be almost equally important parameter instead of average flow rate. CONCLUSIONS The study suggests that average/peak flow rate combined with total prostate volume can be used for prediction of obstruction. The developed probabilistic model helps to determine patients who need invasive urodynamic testing for decision on surgical treatment.