A urine culture is a test that confirms whether a urinary infection is present. It also confirms the microorganism responsible for the infection, which helps to guide treatment.
To complete this test, you should collect the first urine in the morning, being sure to discard the first stream of urine. A urine culture can also be completed with urine collected at another time of the day, however.
Normally, a urine culture will be completed alongside an antibiogram, although the lab will only complete this additional test if the urine culture is positive. The antibiogram tests that bacteria found against several antibiotics to determine which ones it is sensitive or resistant to. This helps the doctor to select the best antibiotic for treatment.
What it tests
The urine culture test determines whether a urinary tract infection (like cystitis, urethritis or pyelonephritis) is present. It helps to identify the microorganism responsible for the infection. The urine culture test is ordered by the doctor when the patient presents with symptoms,like:
- Pain and burning with urination
- Vaginal or penile discharge
- Very dark urine
- Low urinary output
- Bladder heaviness
- Genital itching and/or redness
- Foul-smelling urine
The results of the urine test confirm the infectious agent responsible for the symptoms, which helps to determine the most adequate treatment. The doctor will likely prescribe antibiotics to treat the infection. Learn about about the UTI symptoms that may prompt the doctor to order a urine culture test.
A urine culture test can be completed by any person. Doctors will usually order it for women who are pregnant, as a UTI that is left untreated increases the risk for miscarriage.
How the test is done
It is important to take some factors into consideration when collecting and storing the urine specimen, to avoid any possible changes to the results. To collect urine, you should:
- Wash the genital area with soap and water
- Separate the vaginal labia or retract the penile foreskin
- Discard the first stream of urine in the toilet.
- Then collect the remaining urine in the lab-specified sterilized container.
Urine can sit at room temperature for up to 2 hours, however specimen should be submitted to the lab as soon as possible to ensure accurate results. The specimen should be sterile and obtained from the lab or doctor’s office. After urine is collected, close the container quickly and submit to your doctor or lab immediately.
Another way to collect a urine culture test is to use a sterile in-an-out catheter. This method is best to reduce the amount of possible contaminants, however it is usually only done when the patient is admitted to the hospital.
Positive urine cultures will prompt a further antibiogram test, which will identify the antimicrobrial (e.g. antifungal or antibiotic medication) that is best for treatment.
Urine culture in babies
Because they have a developing immune system and urinary system, babies have UTIs more frequently than adults. This is also due to the fact that babies remain in contact with urine or feces present in the diaper.
A urine cultures may also be ordered for a babies. Urine is collected a few different ways, depending on the baby’s age and general health status. Some methods include a urine collection bag, an in-and-out catheter, or a suprapubic puncture, the last 2 which are more invasive and painful for the baby.
Interpreting results
Urine culture results can be:
- Negative or normal, when there is little to no growth of bacterial colonies in the urine
- Positive when over 100,000 cfu/ml of bacteria grow in the specimen. The test will also reveal the type of bacteria noted.
If an antibiogram is ordered for a positive test, the result will report not only the bacteria present, but the antibiotics the bacteria is sensitive or resistant to.
In some cases, when the urine is not collected or stored properly, other results may be noted:
- False positive: This occurs when the specimen has been contaminated by other microorganisms, blood or medication
- False negative: This can occur when urine pH is acidic (below 6) or when the patient is taking an antibiotic or diuretic
The result may also be doubtful if colonies are present, but less than 100,000 cfu/ml / mL. The test may need to be repeated in this case, as a test is usually positive with a colony count of over 100,0o0 cfu/ml.
Doctors should assess other signs of symptoms if a UTI is confirmed, so that treatment can address all of these.
Other urine tests
Although the urine culture is the main test for confirming a UTI, a routine and microscopy (R&M) urine test can also indicate the presence of an infection. This test confirms the presence of bacteria, leukocytes, epithelial cells, blood, nitrites and hyphae in the urine. The lab can also report on the color and odor of the urine.
This test combined with a thorough assessment may be enough to identify a UTI, without ordering a urine culture. The advantage of a urine R&M is that is an easier, faster test, while a urine culture can take up to 3 days to report.
Nonetheless, urine cultures are necessary mainly to identify the type of antibiotic to use for treatment. The culture is also helpful for cases of recurrent UTIs, in which identifying the underlying bacteria is essential for treatment. The urine culture should ideally be ordered by pregnant women, older adults, and post-surgical patients, or whenever a UTI is suspected.
