Pre-selection of patients for pressure flow analysis based on the maximum flow rate

Objective: To study the effects of the application of flow rate prescreening to select men for invasive pressure-flow studies, notably the reduction of invasive pressure-flow measurements that can be achieved and the proportion of men in whom, on the basis of the application of a prescreening, an invasive measurement is unjustly not indicated (false negatives). In addition, the variables on which these effects depend are studied. Materials and Methods: Two hundred and sixty-two pressure-flow measurements in 131 patients (2 measurements/patient) and 89 free-flow measurements that preceded the invasive measurements in some patients were studied. A mathematical model was developed based on the outcomes of the invasive measurements. By means of the model the effects of several flow rate prescreening scenarios were estimated. A comparison of the model predicted and actually observed effects of flow rate prescreening was made for those measurements that were preceded by a free-flow rate measurement. Results: The application of a free-flow rate prescreening may result in a reduction of the number of invasive measurements of 20-30% at a 5% false negative rate. The reduction that may be achieved at an assumed constant false negative rate depends on the distribution of the maximum flow rate in the population and on the definition of bladder outlet obstruction used. When the measurement selection procedure was applied to the free-flow rate measurements that were available in 89 patients, a 21% reduction in invasive measurement indications was found (25% expected). Four patients (4.5%) would have been unjustly excluded from invasive procedures (maximally 5% expected), three of these four patients were borderline obstructed. Conclusion: Considering the bother and risk to the patient and the cost of invasive measurements we think that a 20-30% gain in efficiency at a 5% risk of unjustly declaring a patient unobstructed makes a flow rate prescreening procedure cost effective in the diagnosis of bladder outlet obstruction.

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