Urinary bladder characteristics via ultrasound as predictors of acute urinary retention in men with benign prostatic hyperplasia

OBJECTIVE: To determine the clinical utility of urinary bladder and prostate characteristics measured by ultrasound scan in predicting acute urinary retention (AUR) for men with bladder outlet obstruction with an underlying benign prostate hyperplasia (BPH).
MATERIALS AND METHODS: Consecutive men aged ≥50 years presenting with lower urinary tract symptoms (LUTS) or AUR were prospectively recruited in this cross-sectional study. International prostatic symptom score (IPSS) and serum prostate-specific antigen (PSA) were recorded. High-resolution ultrasound was used to measure bladder detrusor thickness (DT, mm), prostatic volume (PV, cm3), intravesical prostatic protrusion (IPP, mm), bladder wall thickness (BWT,mm), intravesical volume and bladder radius. The latter two parameters were used to estimate bladder weight (UEBW, g), assuming a spherical bladder.
RESULTS: Among selected patients, thirty had AUR while 32 men presented with LUTS only. There were significant differences between those with and without AUR in their age (70.5 vs 66.0, p=0.017), IPSS (24.0 vs 18.5, p=0.009), serum PSA (6.18 vs 1.77, p=0.002), PV (56.7 vs 32.4, p=0.006), BWT (5.0 vs 4.4, p=0.034) and UEBW (39.1 vs 25.0, p=0.0003). Multivariate analysis revealed high IPSS and UEBW to be predictors for AUR. UEBW was the strongest predictor of AUR: area under ROC curve was 0.767, with sensitivity and specificity of 63.3% and 87.5%, respectively, at cut-off point of 35 g. The likelihood ratio for AUR was also best with UEBW≥35 g.
CONCLUSIONS: Combined with IPSS, ultrasound determined bladder characteristic, particularly UEBW, is a useful tool in predicting AUR in men with BPH.