The value of symptom score, quality of life score, maximal urinary flow rate, residual volume and prostate size for the diagnosis of obstructive benign prostatic hyperplasia: a urodynamic analysis.

PURPOSE: We investigated which linear combination of scores for symptoms, quality of life, maximum urinary flow rate, residual volume and prostate size best discriminated men with prostatism who do and do not have obstruction.
MATERIALS AND METHODS: Mandatory and recommended tests were performed in 196 men older than 50 years with prostatism. Schäfer's obstruction grade was estimated by urodynamic studies. Relative residual volume was defined as residual volume divided by cystometric capacity (times 100%). Correlation coefficients among the different parameters were estimated. Obstruction grade was correlated with linear weighted combinations of the parameters.
RESULTS: Of the men 79% appeared to have obstruction. The formula, prostate size (cm.3) -3 x maximum urinary flow rate (ml. per second) + 1/4 of relative residual volume (%), correlated almost maximally with obstruction grade. Including quality of life score or symptom score in this expression had a negative outcome on the correlation. Calculation of this expression resulted in the bladder outlet obstruction number. In more than 50% of the men the bladder outlet obstruction number was greater than -2 and more than 90% had obstruction. In 25% of all men the bladder outlet obstruction number was greater than 13 and more than 95% had obstruction.
CONCLUSIONS: Bladder outlet obstruction number may be calculated with an easy to use expression composed of prostate size, maximum urinary flow and relative residual volume. In 50% of the men with prostatism bladder outlet obstruction number will diagnose obstruction with a reliability of more than 90%.