Assessment of noninvasive predictors of bladder outlet obstruction and acute urinary retention secondary to benign prostatic enlargement

Purpose: To prospectively compare the diagnostic accuracy of intravesical prostatic protrusion (IPP), detrusor wall thickness (DWT), prostate volume (PV) and serum prostate specific antigen (PSA) levels for detecting bladder outlet obstruction (BOO) and predicting acute urinary retention (AUR) secondary to benign prostatic obstruction.

Patients and methods: In all, 135 men who presented with lower urinary tract symptoms due to benign prostatic enlargement were enrolled in the study; among them, 50 presented with AUR. Thirty normal men in the same age group were included and represented a control group for normative data. Their evaluation included a digital rectal examination, International Prostate Symptom Score and quality-of-life question, uroflowmetry and serum total PSA assay. Transabdominal ultrasonography was used to measure the PV, IPP DWT and post-void residual urine volume. Pressure-flow urodynamic studies were used as the reference standard test for BOO, differentiating obstructed from unobstructed bladders. DWT, IPP, PV and total PSA level served as index tests. To compare the usefulness of the various indices, the area under the curve (AUC) of receiver-operator characteristic curves was calculated for each index.

Results: According to presentation and urodynamic studies, patients were classified into three groups: Group 1 (no BOO), 50 patients with a BOO index (BOOI) of <40; group 2 (BOO), 35 with a BOOI of >40; and group 3 (AUR), 50 who presented with AUR. The IPP, DWT, PV and PSA levels differed significantly between obstructed and unobstructed patients, with a significant correlation with the BOOI. The AUC for IPP, DWT, PSA and PV were 0.885, 0.783, 0.745 and 0.678, respectively. The IPP threshold at 8 mm provided the best diagnostic accuracy (80%) for detecting BOO, followed by combined DWT and IPP (77.6%). Between patients with and without AUR, there was a highly significant difference in IPP, DWT and PSA; a combined IPP threshold of >8 mm and DWT >2 mm detected AUR in 45 of 50 patients (90%).

Conclusion: All four noninvasive indices were correlated significantly with BOOI. The IPP as a single variable and combined with DWT predicted BOO and AUR better than PSA or PV.