After you void (pee) on your own, there can be some urine (pee) left in the bladder. If there is a large amount of urine left and it happens many times, this can be a problem. This is called incomplete bladder emptying, or urinary retention.

There is a test used to measure how much urine is left in your bladder after you void. The test is called a post-void residual. Post-void means after voiding, and residual means what remains. A post-void residual can be measured with an ultrasound, a bladder scanner, or by draining the residual with a catheter. If the amount of urine left in the bladder is high, it is called a high post-void residual.

Some people with high post-void residuals never feel empty and may leak (overflow incontinence). This can be upsetting and embarrassing. For some people, the bladder doesn't empty at all. If this continues, it can cause discomfort, infections, and may affect the health of the kidneys.​