The amount of leftover (residual) urine can be measured by draining the bladder with a thin flexible tube (catheter) or by using ultrasound. The catheter method has a slight risk of causing infection or injury to the tube leading from the bladder (urethra). But the catheter method is safe when done carefully. And it may be less expensive than ultrasound.
Medical Review:E. Gregory Thompson MD - Internal Medicine & Adam Husney MD - Family Medicine & J. Curtis Nickel MD, FRCSC - Urology