The value of measuring the prostatic resistive index vs. pressure-flow studies in the diagnosis of bladder outlet obstruction caused by benign prostatic hyperplasia

OBJECTIVE To compare the prostatic resistive index (RI) and measurements from pressure-flow studies (PFS) for the diagnosis and follow-up of bladder outlet obstruction (BOO) in patients with benign prostatic hyperplasia (BPH). PATIENTS AND METHODS In all, 338 men (aged 55-82 years) presenting with lower urinary tract symptoms were evaluated prospectively for BOO secondary to BPH. In all patients, the prostatic RI was measured by transrectal power Doppler ultrasonography. PFS were assessed in all patients and depending on the results the patients were divided into an obstructive and an unobstructive group. The receiver operating characteristic (ROC) curve was used to determine the prostatic RI threshold value for predicting BOO secondary to BPH. Patients who were confirmed to have BOO secondary to BPH received either medical or surgical treatment, and they were re-evaluated after 3 and 6 months with prostatic RI measurements. RESULTS According to the PFS the obstructive group included 158 patients and the unobstructive group 180 patients. The mean (SD) prostatic RI was significantly higher in the obstructive group, at 0.73 (0.04), than in the unobstructive group, 0.65 (0.05) (P < 0.001). Using the ROC curve a prostatic RI of ⩾ 0.71 predicted BOO secondary to BPH, with 84.6% sensitivity, 78.4% specificity and 83.8% overall predictability. After management, the prostatic RI of the obstructive group, 0.69 (0.08), was significantly lower than before treatment, 0.73 (0.04) (P < 0.05). CONCLUSIONS The prostatic RI can predict BOO with high specificity and sensitivity. We believe that the prostatic RI could be a useful variable for the diagnosis and follow-up of patients with BPH.