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 urinar y tract symptoms, transrectal ultrasound measurement and the bladder outlet obstruction index, as derived from pressure flow studies. We also develope d and validated a multivariate analysis for predicting the bladder outlet o bstruction index. Materials and Methods: We evaluated 384 men with lower urinary tract sympto ms using the International Prostate Symptom Score, maximum urine flow, post -void residual urine, transrectal ultrasound and urodynamic studies. Data w ere analyzed by multiple linear regression with continuous variables. A sim ple algorithm, that is the predicted bladder outlet obstruction index, was created using the best fit variables identified from a derivation set and a ssessed in a separate validation set. The predicted index was applied to pr edict 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 ther e was a 92% risk or positive predictive value of equivocal or worse obstruc tion, 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 max imum urine flow and prostate volume. Development of the predicted bladder o utlet obstruction index algorithm enables the mathematical prediction of ob struction from these simple measures. Using the predicted bladder outlet ob struction index clinicians can determine the risk of obstruction in individ uals. In 65% of patients we predicted equivocal or worse obstruction with g reater than 90% confidence.