Post-void residual (PVR) of urine is a common part of the routine clinical assessment in males with lower urinary tract symptoms (LUTS) (1). Post-void residual of urine can be measured by transabdominal ultrasound (US), bladder scan (BS) or catheterisation. A missing established PVR threshold for treatment decision is the main limit of this parameter, due to large test-retest variability and lack of outcome studies. Moreover, the diagnostic accuracy of PVR is low. The use of a PVR threshold of 50 mL has a positive predictive value (PPV) of 63% and a negative predictive value (NPV) of 52% as a predictor of bladder outlet obstruction (BOO)(2). The identification of at risk patients for acute urinary retention (AUR) may be achieved monitoring the changes over time of PVR measurements(3). Furthermore, in patients with lower urinary tract symptoms, high baseline PVR is associated with an increased risk of symptom progression 
Aim of this study was to assess the role and the values of the preoperative PVR in males underwent transurethral resection of the prostate (TURP) for LUTS and the related outcomes after the procedure.

This is a prospective ongoing study started in January 2017 involving males with LUTS candidates for TURP. The medical and urological history was recorded in all the population. Both preoperative evaluation and the 1-year follow-up consisted in: peak flow (Qmax), PVR, PVR-ratio as the ratio of PVR to bladder volume (BV: voided volume + PVR), and the International Prostate Symptoms Score Questionnaire (IPSS). Patients were also distributed in groups according to preoperative PVR thresholds: i) PVR 0-50ml; ii) PVR 51-100ml; iii) PVR 101-150ml; iiii) PVR 151-200ml; iiiii) PVR>200ml. Statistical analysis was performed using T-test, Wilcoxon test, one-way ANOVA test, Kruskal-Wallis Test.

Data were complete in 52 patients, with a mean age of 68.9+8.5 yrs. A significant improvement in voided volume, Qmax, PVR, IPSS score was documented. Mean voided volume was 214.8 ml (sd 102.1 ml) and 301.0 ml (sd 335.9 ml) respectively preoperative and postoperative. Mean Qmax was 9.7 ml/s (sd 4.2 ml/s) and 19.5 ml/s (sd 10.2 ml/s) respectively preoperative and postoperative. Mean post-void residual of urine was 120.5 ml (sd 125.9 ml) and 25.8 ml (sd 25.4 ml) respectively preoperative and postoperative. Mean preoperative PVR ratio was 31.1% (ds 22.3%) ml) and 9% (ds 8.8%) postoperative. Mean preoperative IPSS scores was 22.6 (sd 7) and 8.7 (sd 6) postoperative. The majority of the males showed a PVR < 100ml (59.6%), while the remaining 21/52 patients (40.4%) had a PVR >100ml. No significant difference was found in Qmax and IPSS score among the groups, in both preoperative and postoperative assessment (Table 1). In each group we found a significant improvement in Qmax and IPSS score after transurethral resection of the prostate (Tables 2). Table 2 shows also how post-void residual of urine decreased significantly after TURP in all the groups except in the Group i (PVR 0-50ml). This finding may be related to the low preoperative post-void residual of urine.

Only a minor part of the males showed a high preoperative post-void residual of urine (>100ml), therefore PVR did not have a crucial role in the decision-making. Quite the reverse, Qmax and symptoms score had the main influence. Post-void residual of urine was not correlated to preoperative and postoperative Qmax and IPSS. This finding suggests that post-void residual of urine was a poor predictive factor for the decision-making and outcomes in males candidates for transurethral resection of the prostate.

In our cohort a high post-void residual of urine was present only in a minority of patients candidates for transurethral resection of the prostate and did not significantly influence the outcomes of TURP. This study confirmed that post-void residual of urine is still a controversial and poor reliable parameter in the evaluation of males with lower urinary tract symptoms. as well in the treatments’ decision-making.

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