If you experience symptoms of a UTI, such as pain during urination, the need to urinate more frequently or cloudy urine.
A mid-stream "clean" urine sample
Generally none, but you may be instructed not to urinate for at least one hour before the test and/or to drink a glass of water 15-20 minutes before sample collection.
Urine is one of the body’s waste products. It is produced in the kidneys and collected in the bladder until a person urinates. Normally, the urine does not contain significant numbers of any microorganism. However, if bacteria or yeast are introduced into the urinary tract, they can multiply and cause a urinary tract infection, called a UTI.
Most UTIs are caused by Escherichia coli (E. coli), one of the most common bacteria found in the human bowel. Other frequently identified bacteria are Proteus, Klebsiella, and Staphylococcus saprophyticus.
If bacteria are detected in the urine, they will then be tested for their antibiotic susceptibility so that an effective treatment can be administered.
How is the sample collected for testing?
A “mid-stream” urine sample is necessary for a culture so bacteria present around the urethra and on the hands are not introduced. The procedure for collecting a clean “mid-stream” includes the following steps:
- Hands should be washed just before beginning the collection.
- In females, hold the labia apart whilst urinating..
- Do not collect the initial stream of urine since it may be contaminated with skin and urethral cells and bacteria.
- Midway through the urination process, collect a sample of urine in a sterile screw-top container (hence the name “mid-stream” urine).
- Tightly cap the container and wash your hands again..
- The sample should be taken to the laboratory as quickly as possible to prevent the further growth of organisms.
- Store the sample in the refrigerator if you cannot deliver the sample the same day.
Uncontaminated specimens can also be obtained from catheterised patients following the same hygienic procedures for the end of the catheter. Urine can also be collected directly from the bladder using a needle and syringe in a process known as a suprapubic aspiration, but this is usually reserved for infants and young children where it has been difficult to obtain a reliable mid-stream urine sample.
A sample of the urine is then spread across the surface of one or more agar plates and placed in an incubator at body temperature overnight. If there is no growth on the agar plates at the end of that time, the culture is considered negative for significant number of microorganisms that could cause an infection. If bacteria or yeast are present, the total number of organisms is counted (colony count), and they are identified by additional biochemical or molecular testing. Further tests will determine which antibiotics are likely to be effective in treating the infection.
Is any test preparation needed to ensure the quality of the sample?
Generally none; however, you may be instructed not to urinate for at least an hour before the test and/or to drink a glass of water 15-20 minutes before sample collection. This will help to ensure that you can produce enough urine for the sample. Follow the instructions provided for collecting a clean catch urine sample.
How is it used?
When is it requested?
If you have symptoms which indicate the possibility of a urinary tract infection, such as pain and burning when urinating and frequent urge to urinate, your doctor would usually perform a rapid urinalysis ‘dipstick’ test on the urine sample and if this indicates that you may have a UTI, they will send the sample to the laboratory for further tests. In the laboratory, the sample will be screened by microscopy (or using an automated system) for the presence of red and white blood cells, bacteria, yeast and other microscopic structures. Culture is used when the microscopy result indicates that there may be infection, for example if it contains a raised number of white blood cells. In addition, culture may be used for certain groups of patients who may not show obvious symptoms of an infection, such as pregnant women, children or immunocompromised patients.
What does the test result mean?
A negative culture usually means that there is no infection. However, a culture may be repeated in 1-2 days if the symptoms persist.
The presence of bacteria, as indicated by a positive culture, usually indicates an infection. Any bacterial infection may be serious and can spread to other areas of the body if not treated. Since pain is often the first indicator of an infection, prompt treatment, usually with antibiotics, will help to alleviate the pain.
Is there anything else I should know?
Females get UTIs more often than males. Even school-age females may have frequent UTIs. For males with a culture-proven UTI, the doctor may request further tests to rule out the presence of a kidney stone or a structural abnormality of the urinary tract that could cause the infection.
The surgery called to say they need another fresh urine sample because the first sample was contaminated. What happened?
If the first part of the urine flow was collected instead of the mid stream urine (see above), the urine culture may grow a number of different types of bacteria and is assumed to be contaminated. The culture will be discarded because it cannot be determined if the bacteria originated inside or outside the urinary tract. A contaminated specimen can be avoided by following the directions by collecting a mid-stream sample. Pregnant people may find it difficult to collect a mid stream sample easily.
My doctor said I had symptoms of a urinary tract infection and prescribed antibiotics without waiting for the results of the culture. Why?
The reason is because bacteria known as E. coli cause the majority of lower urinary tract infections. This organism is usually susceptible to a variety of antibiotics, such as trimethoprim or nitrofurantoin. Your doctor may start you on one of these antibiotics to relieve your symptoms while waiting for results from the culture.