Combination of symptom score, flow rate and prostate volume for predictingbladder outflow obstruction in men with lower urinary tract symptoms

Purpose: The severity of lower urinary tract symptoms associated with benig n prostatic enlargement correlates poorly with bladder outlet: obstruction. Since urodynamic studies are presumed to be relatively complex, invasive a nd not cost-effective, they are not routinely performed by physicians treat ing men with lower urinary tract symptoms. As a result, a large number of p atients are treated for bladder outlet obstruction when in fact obstruction may not be present. Since other noninvasive methods have not been effectiv e for predicting bladder outlet obstruction, we investigated whether a comb ination of prostate volume, uroflowmetry and the American Urological Associ ation (AUA) symptom index would be reliable for predicting this condition. Materials and Methods: We prospectively evaluated 204 men with a mean age p lus or minus standard deviation of 66.7 +/- 7.5 years who presented with lo wer urinary tract symptoms. Each patient completed an AUA symptom index que stionnaire and underwent uroflowmetry, post-void residual urine volume meas urement, pressure flow study and transrectal ultrasound of the prostate to estimate prostatic volume. We constructed receiver operating characteristic s curves using various threshold values for maximum urine flow and prostate volume. Threshold values for maximum urine flow and prostate volume were u sed alone and combined with the AUA symptom index for predicting bladder ou tlet obstruction. We selected a cutoff value for maximum urine flow of 10 o r less mi. per second and prostate volume of 40 gm. or greater, and used th ese values with an AUA symptom index of greater than 20 to predict bladder outlet obstruction in the group overall. Results: Differences in the mean symptom index score in men with and withou t bladder outlet obstruction were not statistically significant. There was no obstruction in 19%, 28.9% and 35% of those with severe, moderate and mil d symptoms, respectively. The selected cutoff values of maximum urine flow, prostate volume and symptom score combined correctly predicted obstruction in all 39 patients. Therefore, our combination of cutoff values proved to be highly accurate for predicting bladder outlet obstruction. Sensitivity, specificity, and positive and negative predictive values were 26%, 100%, 10 0% and 32%, respectively. Conclusions: Our study showed that combining the AUA symptom index, maximum urine flow and prostate volume reliably predicted bladder outlet obstructi on in a small subset of patients only. Although bladder outlet obstruction was correctly predicted by our threshold values of AUA symptom index, maxim um urine flow and prostate volume in only 39 men (26%) with obstruction, th ese patients represent a substantial group in any large urological practice treating male lower urinary tract symptoms.