Weak correlation between bladder outlet obstruction and probability to void to completion

OBJECTIVES: To investigate the weak correlation between bladder outlet obstruction (BOO), as diagnosed using the provisional International Continence Society nomogram for the definition of BOO in men, and postvoid residual urine volume. METHODS: The relationship between voiding to completion and several indexes for bladder outlet resistance and bladder contractility was studied in 131 pressure flow studies in male patients using multivariate logistic regression analysis. RESULTS: The International Continence Society nomogram and the related BOO index weakly predict for postvoid residual urine volume (areas under the receiver operating characteristic curve 0.63 and 0.64, respectively). The BOO index primarily measures bladder outlet resistance. If the nomogram or BOO index is augmented with bladder contractility information, the postvoid residual urine volume can be predicted significantly better (eg, area under the receiver operating characteristic curve [0.89] for the combination of the BOO index and bladder contractility information). CONCLUSIONS: The weak correlation between BOO and postvoid residual urine volume is related to the fact that emptying the bladder to completion depends on bladder contractility, as well as bladder outlet resistance. It is possible to estimate the probability to void to completion quite accurately on the basis of bladder outlet resistance and bladder contractility. We named this probability "relative bladder outlet resistance." A high probability of a postvoid residual urine volume may be assumed to indicate "relative BOO." By its very nature, the correlation between "relative BOO" and postvoid residual urine volume is good

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