**6.8 Post-void residual urine evaluation**

Post-void residual urine volume can be measured with sufficient accuracy noninvasively by transabdominal ultrasonography. The measurement variation caused by the method is less than the biologic range of PVR variation (McConnell, Barry et al. 1994). It may also be measured by invasive methods (catheterization).

It has been well described that large residual urine volumes (>300 mL) affect renal function in advanced BPH (Neal, Styles et al. 1987; Rule, Jacobson et al. 2005). A PVR of more than 100 mL is defined as chronic urinary retention which is significantly associated with CKD in community-dwelling men (Rule, Jacobson et al. 2005). Nevertheless, small residual urine volumes (<100 mL) may also affect renal function as the presence of PVR relates with renal function regardless of the quantity of PVR (Yamasaki, Naganuma et al. 2011). Thus ultrasonographic evaluation of post-void residual is a useful test in the prevention of CKD secondary to BPH. Chronic urinary retention is related with CKD (Rule, Jacobson et al. 2005).
