Test Overview
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 about
60 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.)
How It Feels
Collecting a urine sample is not painful.
Risks
Collecting a urine sample does not cause problems.
Results
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.
Urine culture| Normal: | No bacteria or other germs (such as
fungi) grow in the culture. The culture result is
negative. |
|---|
| Abnormal: | 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.
References
Other Works Consulted
- Chernecky CC, Berger BJ (2008). Laboratory Tests and Diagnostic Procedures, 5th ed. St. Louis: Saunders.
- Fischbach FT, Dunning MB III, eds. (2009). Manual of Laboratory and Diagnostic Tests, 8th ed. Philadelphia: Lippincott Williams and Wilkins.
- Pagana KD, Pagana TJ (2010). Mosby's Manual of Diagnostic and Laboratory Tests, 4th ed. St. Louis: Mosby Elsevier.
Credits
ByHealthwise Staff
Primary Medical ReviewerE. Gregory Thompson, MD - Internal Medicine
Adam Husney, MD - Family Medicine
Specialist Medical ReviewerElizabeth T. Russo, MD - Internal Medicine
Current as ofMarch 3, 2017