Residual urine is urine left in the bladder after a person has urinated. Voiding the whole contents of the bladder is generally a good idea, when you can. Sometimes people who leave residual urine in the bladder are suffering from poor bladder muscular tone, or from conditions that restrict the flow of urine, like an enlarged prostate or bladder stones.

The difficulty in not voiding the bladder entirely is that urine remaining in the bladder can become a good culture for bacterial growth. People who frequently leave residual urine in the bladder may be at much greater risk for urinary tract infections (UTI). UTIs can create more residual urine, because voiding the bladder may be difficult, painful, or the urine stream can become partially obstructed.

When people are unable to fully clear their bladders, and leave residual urine, they also may feel the need to urinate more often. Any new urine entering the bladder combines with the residual urine to fill the bladder quickly. This can lead to poor nights of sleep, lots of bathroom breaks, and also the uncomfortable feeling that the bladder is never fully empty.

When people have UTIs on a regular basis, doctors may want to evaluate the bladder to measure residual urine. This is easily accomplished by measuring the urine level through sonogram, after a person has urinated. Unfortunately, a sonogram may not always work, since visualizing the pelvic region is much easier when a person has a full bladder. People who are significantly overweight may not be able to be tested in this manner. In this case, computerized axial tomography (CAT) scans may be used instead.

It’s important to pay attention to the frequency of UTIs since they can suggest other conditions. In men, particularly as they age, problems with residual urine can indicate enlarged prostate and prostate cancer. In women and men, poor muscle tone in the bladder may suggest bladder cancer, which is fairly uncommon. In any case, when one urinates, it’s a good idea to make sure to urinate as fully as possible, so that little residual urine remains in the bladder.

Doctors suggest that you wait a few moments before leaving the bathroom, and try urinating again if you've had problems in the past with residual urine. Often, waiting just a minute or two before trying again can help clear residual urine. This is always good advice if you have frequent UTIs that are not caused by any known physiological problems. Fully voiding the bladder may help reduce their incidence.

If you have problems with residual urine or any health concerns, you should get advice from a doctor or other qualified health care professional.