Unravelling detrusor underactivity: Development of a bladder outlet resistance—Bladder contractility nomogram for adult male patients with lower urinary tract symptoms

Aims Voiding dysfunction in adult men may be caused by bladder outlet obstruction (BOO) and/or detrusor underactivity (DU). Until now, it is only possible to classify BOO and DU by pressure‐flow analysis. Low values of the maximum Watts factor (W max ) indicate DU but thresholds for the diagnosis have not been established. Purpose of this study was to construct a nomogram using bladder outlet resistance and detrusor contractility in order to classify BOO and DU simultaneously. Methods Treatment naïve men aged ≥40 years with uncomplicated lower urinary tract symptoms (LUTS) were prospectively evaluated. Patients were assessed with IPSS, prostate volume, uroflowmetry, post‐void residual, and pressure‐flow measurement. The bladder outlet obstruction index (BOOI) was used to determine BOO‐grade and W max to calculate detrusor contractility. Individual BOOI‐W max values were plotted in a graph. Linear interpolation was applied to determine the 10th, 25th, 50th, 75th, and 90th percentiles. Results Retrospective analysis of 822 male patients with means of 64 years, IPSS 16, and prostate volume of 40 cc. Patient and clinical parameters of the <25th percentile groups were significantly different compared to the 25th–50th percentiles: age (66 vs. 63 years, P = 0.006), bladder capacity (503 vs. 442 ml, P = 0.009), post‐void residual urine (167 vs. 116 ml, P = 0.001), and voiding efficiency (67% vs. 73%, P = 0.015). Conclusions The nomogram quantifies the relationship between detrusor contractility and BOO in men with LUTS. A measurement value <25th percentile correlates with clinical indicators of DU and is proposed as a cut‐off value for DU‐diagnosis. Higher age, bladder capacity, and PVR as well as lower voiding efficiency indicate DU. Neurourol. Urodynam. 35:980–986, 2016 .