Bladder Outlet Obstruction Number

Patient population:

(1) males over 50 years of age

(2) no exclusion criteria present

(3) voided > 150 mL of urine during a free uroflowmetry study

bladder outlet obstruction number =

= (prostate volume in cubic cm) - (3 * (maximum urinary flow rate in mL per second)) + (0.25 * (relative residual volume in percent))

where:

• The relative residual urine volume is the residual urine volume divided by cystometric capacity multiplied by 100 and expressed in percent.

• The filling cystometric studies are performed with the urinary bladder filled with saline at 37°C through a catheter at a constant rate of 50 mL per minute.

• The residual urine volume is determined by transabdominal ultrasonography.

• The maximal urinary flow rate is estimated from at least 2 uroflowmetry measurements with a voided volume ideally greater than 150 mL.

Interpretation:

• The bladder outlet obstruction number usually ranges from about -80 to +80.

• The bladder outlet obstruction number correlates with the obstruction grade.