A probability based system for combining simple office parameters as a predictor of bladder outflow obstruction

Purpose: We explored the relationships of office assessment of lower urinary tract symptoms, transrectal ultrasound measurement and the bladder outlet obstruction index, as derived from pressure flow studies. We also developed and validated a multivariate analysis for predicting the bladder outlet obstruction index. Materials and Methods: We evaluated 384 men with lower urinary tract symptoms using the International Prostate Symptom Score, maximum urine flow, post-void residual urine, transrectal ultrasound and urodynamic studies. Data were analyzed by multiple linear regression with continuous variables. A simple algorithm, that is the predicted bladder outlet obstruction index, was created using the best fit variables identified from a derivation set and assessed in a separate validation set. The predicted index was applied to predict the probability of actual obstruction according to office parameters. Results: Maximum urine flow and total prostate volume predicted the bladder outlet obstruction index most completely (adjusted R-2 = 0.50, F 75.9, p <0.0001), while other variables were not helpful. These variables were used to create the predicted bladder outlet obstruction index algorithm, antilog(10) (2.21 - 0.50 log maximum urine flow + 0.18 log total prostate volume) - 50. In the 42% of patients with a predicted index of greater than 40 there was a 92% risk or positive predictive value of equivocal or worse obstruction, whereas a predicted index of less than 20 in 23% indicated a 4% risk of significant obstruction. Conclusions: The bladder outlet obstruction index can be predicted from maximum urine flow and prostate volume. Development of the predicted bladder outlet obstruction index algorithm enables the mathematical prediction of obstruction from these simple measures. Using the predicted bladder outlet obstruction index clinicians can determine the risk of obstruction in individuals. In 65% of patients we predicted equivocal or worse obstruction with greater than 90% confidence.