At a Glance
Why Get Tested?
When to Get Tested?
The Test Sample
What is being tested?
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?
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 from front to back, holding the labia apart.
- Do not collect the initial stream of urine since it may be contaminated with skin and urethral bacteria.
- Midway through the urination process, collect collect 20-30 millilitres of urine in a sterile screw-top container (hence the name ‘mid-stream’ urine).
- Tightly cap the container, wash your hands thoroughly and label the container.
- 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 initially assessed under microscope in a counting chamber and visible cells are counted. The presence of large numbers of white blood cells (‘pus cells’) is strongly indicative of a UTI. Appreciable numbers of squamous epithelial cells indicate a poorly collected specimen. The small amount of urine (usually 10 microlitres) is then cultured and inoculated plates are 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 growing, the total number of organisms is counted (colony count), and the organisms are identified by additional biochemical testing. The actual number of bacteria present in the sample usually helps to distinguish between infection and contamination to be made. The concentration of viable bacteria in a urine sample is usually expressed in colony forming units per litre (CFU/L). If greater than 108 CFU/L of a recognised uropathogen (for example Escherichia coli or Proteus vulgaris) are present in a specimen, this is considered to be reliable evidence of the presence of a urinary tract infection. However, this rule has been validated for uncomplicated urinary tract infections in adult women and clinical reasoning should be employed when interpreting urine culture results from men and symptomatic children.
Further tests determine which antibiotics are likely to be effective in treating the infection.
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NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used.