Post-voided residual urine ratio as a predictor of bladder outlet obstruction in men with lower urinary tract symptoms: development of a clinical nomogram

Purpose: To confirm the correlation between post-void residual urine ratio (PVR-R) and BOO diagnosed by pressure-flow studies (PFS) in males with lower urinary tract symptoms (LUTS) and to develop a clinical nomogram. Methods: A consecutive series of patients aged 45 years or older with non-neurogenic LUTS were prospectively enrolled. Patients underwent standard diagnostic assessment for BOO including International Prostatic Symptoms Score, uroflowmetry, urodynamic studies, suprapubic ultrasound of the prostate, and ultrasound measurements of the bladder wall thickness (BTW). PVR-R was defined as follows: PVR-R = (PVR/total Bladder Volume [BV]) × 100). Logistic regression analysis was used to investigate predictors of pathological bladder emptying (BOO) defined as Schafer > II. A nomogram to predict BOO based on the multivariable logistic regression model was then developed. Results: Overall 335 patients were enrolled. Overall, 131/335 (40%) presented BOO on PFS. In a multivariable logistic age-adjusted regression model BWT (odds ratio [OR]: 2.21 per mm; 95% confidence interval [CI], 1.57-3.09; p = 0.001), PVR-R (OR: 1.02 per %; 95% CI, 1.01-1.03; p = 0.034) and prostate volume (OR: 0.97 per mL; 95% CI, 0.95-0.98; p = 0.001) were significant predictors for BOO. The model presented an accuracy of 0.82 and a clinical net benefit in the range of 10-90%. Conclusions: The present study confirms the important role of PVR-ratio in the prediction of BOO. For the first time, we present a clinical nomogram including PVR-ratio for the prediction of BOO.