Red blood cells in urine can be a sign of a number of issues involving the bladder and kidneys. In healthy individuals, a few red blood cells are often found in urine samples and are not a cause for concern, but large numbers, or so much blood that the urine appears discolored, are a cause for concern. If red blood cells are found in the course of a urinalysis, other information from the test may provide clues about why, or additional testing may be needed to get to the bottom of the problem.

The formal term for abnormal numbers of red blood cells in urine is hematuria. One potential cause is contamination of the sample, seen when menstruating women provide a urine sample and some of the menstrual blood ends up in the sample. Recent trauma to the urethra, as from a catheterization or injury, can also be a cause of red blood cells in urine. In these cases the underlying cause is known and no additional treatment needs to be taken, as the issue should resolve on its own.

If white blood cells are also present, it is a sign of inflammation or infection along the urinary tract. Red blood cells in urine can also be associated with blockages, stones, or internal injuries; someone who has been kicked or punched in the kidneys, for example, will often start to produce bloody urine as a result of damage to the kidneys. Hard exercise can sometimes be a cause as well, with people like marathon runners sometimes developing bloody urine after a race.

Malignancies can be associated with red blood cells in urine in some cases. In these instances, there may also be traces of cancerous cells sloughed off from the growth and these will be identified by the pathologist. Certain disorders can cause bloody urine and people may also experience it in association with medications. Patients should make sure their complete medical history is available so the doctor can be aware of any obvious underlying causes behind red blood cells in urine.

Once a doctor determines why a patient has bloody urine, treatment can be offered. For something like an infection, this may be as simple as a course of antibiotics. After the treatment is over, another sample will be requested for analysis to make sure the issue has been completely addressed. Sometimes bacteria and blood can be present in the urine without being visible to the naked eye, so even if the urine looks normal, it is important to do a followup urinalysis to avoid a situation where low levels of bacteria are left behind and start growing again, causing a recurrence of infection.