Noninvasive assessment of prostatic obstruction in elderly men with lower urinary tract symptoms associated with benign prostatic hyperplasia.

Objectives: To investigate what combination of easily available parameters allows the noninvasive prediction of infravesical obstruction in optimal agreement with urodynamic classification. Urodynamically, men with lower urinary tract symptoms suggestive of benign prostatic hyperplasia are classified as nonobstructed or obstructed.
Methods: Mandatory and recommended tests were performed in 160 consecutive men with lower urinary tract symptoms suggestive of benign prostatic hyperplasia. The classification of the International Continence Society, the group-specific urethral resistance factor, and Schäfer's obstruction grade were estimated from urodynamic studies. The frequency-volume charts were analyzed. A separate group of 173 consecutive men was used for validation.
Results: The formula, prostate volume (in cubic centimeters) - 3 x maximal urinary free flow rate (in milliliters per second) - 0.2 x mean voided volume (in milliliters; as estimated from frequency-volume charts), was optimal in the classification compared with the urodynamic classification. Extension of this formula to more than three parameters did not result in better selection. As estimated from receiver operating characteristic curves, the accuracy of the formula appeared to be good. The method of quantifying urethral resistance minimally affected the classification that resulted from the combination. From the results, a diagram was created presenting the probability of an individual to have infravesical obstruction. The validation results were satisfactory.
Conclusions: The prediction of the probability of a man with lower urinary tract symptoms suggestive of benign prostatic hyperplasia to have infravesical obstruction can be deduced from a diagram based on a formula composed of three readily available parameters: prostate volume, maximal urinary free flow rate, and mean voided volume.