To diagnose a urinary tract infection (UTI)
If you experience symptoms of a UTI, such as pain during urination
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 human bacteria. Other frequently identified bacteria are Proteus, Klebsiella, and Staphylococcus saprophyticus.
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.
- A soap should be used to clean the penis in males, and females should wash the external genitalia, holding the labia apart.
- Repeat this procedure three times.
- Do not collect the initial stream of urine since it may be contaminated with skin and urethral 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 thoroughly.
- The sample should be taken taken to the laboratory as quickly as possible to prevent the further growth of organisms.
Uncontaminated specimens can also be obtained from catheterised patients following the same hygienic procedures for the end of the catheter.
A sample of the urine is then streaked across the surface of one or more agar plates and placed in an incubator at body temperature for 24 hours. 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 the organisms are identified by additional biochemical testing. Further tests 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?
The culture may be used when symptoms indicate the possibility of a urinary tract infection, such as pain and burning when urinating and frequent urge to urinate. In addition, it may be used for patients who have a catheter inserted for an extended period of time, even if they do not show obvious symptoms of an infection, since there is a risk of bacteria being introduced by the catheter. Pregnant women without any symptoms may be screened for bacteria in their urine, which could harm the baby.
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, 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 order 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 skin and genital area were not cleaned well prior to collecting the sample, 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 to carefully clean yourself and by collecting a mid-stream sample.
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.