A urine culture is a test to find germs (such as bacteria) in the urine that can cause an infection. Urine in the bladder is normally sterile. This means it does not contain any bacteria or other organisms (such as fungi). But bacteria can enter the urethra and cause a urinary tract infection (UTI).
A sample of urine is added to a substance that promotes the growth of germs. If no germs grow, the culture is negative. If germs grow, the culture is positive. The type of germ may be identified using a microscope or chemical tests. Sometimes other tests are done to find the right medicine for treating the infection. This is called sensitivity testing.
UTIs are more common in women and girls than in men. This may be partly because the female urethra is shorter and closer to the anus. This allows bacteria from the intestines to come into contact more easily with the urethra. Men also have an antibacterial substance in their prostate gland that lowers their risk.
Why It Is Done
A urine culture may be done to:
- Find the cause of a urinary tract infection (UTI).
- Make decisions about the best treatment for a UTI. This is called sensitivity testing.
- Find out if treatment for a UTI worked.
How To Prepare
You do not need to do anything before you have this test. If you are taking or have recently taken antibiotics, tell your doctor.
You will need to collect a urine sample. Avoid urinating just before having this test.
Talk to your doctor if you have any concerns about the need for the test, its risks, how it will be done, or what the results will mean. To help you understand the importance of this test, fill out the medical test information form( What is a PDF document? ).
How It Is Done
You may be asked to collect a clean-catch midstream urine sample for testing. The first urine of the day is best because bacterial levels will be higher.
Clean-catch midstream urine collection
This method helps protect the urine sample from germs that are normally found on the penis or vagina.
- Wash your hands before you collect the urine.
- If the collection container has a lid, remove it carefully. Set it down with the inner surface up. Do not touch the inside of the cup with your fingers.
- Clean the area around your genitals.
- For men: Pull back the foreskin, if you have one. Clean the head of the penis thoroughly. Use medicated towelettes or swabs.
- For women: Spread open the folds of skin around the vagina with one hand. Then use the other hand to clean the area around the vagina and urethra thoroughly. Use medicated towelettes or swabs. Wipe the area from front to back to avoid spreading bacteria from the anus to the urethra.
- Start to urinate into the toilet or urinal. Women should keep holding apart the folds of skin around the vagina while they urinate.
- After the urine has flowed for several seconds, place the collection cup into the stream. Collect about60 mL (2 fl oz) of this "midstream" urine without stopping the flow.
- Do not touch the rim of the container to your genital area. And don't get toilet paper, pubic hair, stool (feces), menstrual blood, or other foreign matter in the urine sample.
- Finish urinating into the toilet or urinal.
- Carefully replace the lid on the cup. Wash your hands. Return the cup to the lab. If you are collecting the urine at home and can't get it to the lab in an hour, refrigerate it.
A health professional may collect a urine sample by placing a urinary catheter into the bladder. This method is sometimes used to collect urine from a person in the hospital who is very ill or who can't provide a clean-catch sample. Using a catheter to collect a urine sample reduces the chance of getting bacteria from the skin or genital area in the urine sample.
Collecting a urine sample from a small child or baby may be done by using a special plastic bag with tape around its opening (a U bag). The bag is attached around the child's genitals until he or she urinates (usually within an hour). Then the bag is carefully removed. To collect a urine sample from a very sick baby, a doctor may insert a needle through the baby's belly directly into the bladder. (This is called a suprapubic tap.)
A urine culture is a test to find germs (such as bacteria) in the urine that can cause an infection. Urine culture results are usually ready in 1 to 3 days. But some germs take longer to grow in the culture. So results may not be available for several days.
No bacteria or other germs (such as fungi) grow in the culture. The culture result is negative.
Organisms (usually bacteria) grow in the culture. The culture result is positive.
A count of 100,000 or more bacteria per milliliter (mL) of urine may be caused by an infection. A count ranging from 100 to 100,000 could be caused either by infection or by contamination of the sample. You may need to repeat the urine culture. If the count is 100 or less, infection is unlikely. But you may have a count of 100 or less if you are already taking antibiotics.
If test results are positive, sensitivity testing may be done to help make decisions about treatment.
What Affects the Test
You may not be able to have the test, or the results may not be helpful, if:
- You take antibiotics or have just finished taking them.
- You take water pills (diuretics) or drink a large amount of liquid. This may dilute your urine and reduce the number of bacteria in the sample.
- You take a lot of vitamin C.
What To Think About
- A urine culture done in the early stage of a urinary tract infection (UTI) may be less accurate than one that is done after the infection becomes established.
- A urine culture may be done when an abnormal result from a urinalysis (such as an increased number of white blood cells) shows signs of an infection. To learn more, see the topic Urine Test.
- A urine culture may be repeated after the UTI has been treated. This is to make sure the infection is cured.
- People who have a urinary catheter in place for a long time are at high risk for getting a UTI.
- To diagnose tuberculosis that has spread to the urinary tract, a special test will be done using all of the first morning urine on 3 separate days.
- Sensitivity testing helps your doctor choose the best medicine to treat specific types of bacteria or fungus that may be causing a UTI.
- Some types of bacteria or fungi may take several weeks to grow in the culture.