Urinalysis

Bacteria in urine

Urinalysis
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Bacteria in urine
foto de Fernando Martínez Sáez
Written by

Fernando Martínez Sáez
Medically reviewed by our Medical staff

Last update: 23-09-2021

How else can it be called?

  • Bacteriuria

  • CIE-10: R82.71

Why bacteria can be present in urine?

The presence of bacteria in a urine test is useful for the diagnosis of Urinary Tract Infection (UTI).

Bacteria are not normally present in urine. However, as urine specimens are not collected under sterile conditions, a few bacteria are usually present as a result of vaginal, urethral, external genitalia, or collection-container contamination.

These bacteria may multiply rapidly in specimens that remain at room temperature for extended periods.

Why is this test performed?

It is not uncommon to see a few bacteria in urine specimens, especially in women, but it is not a sign of a pathological condition.

However, a high number of bacteria in the urine may help in the diagnosis of some type of infection.

For example, a high number of bacteria in the urine accompanied by WBCs (White Blood Cells) are usually related to infections of the urinary tract.

The presence of bacteria can be indicative of either lower or upper UTI (Urinary Tract Infection).

How is the test performed?

To study the bacteria under the microscope, it is necessary to obtain the urinary sediment. For this matter, the urine sample should be placed at rest for some hours waiting for the different elements of the urine (white and red blood cells, bacteria, crystals, etc.) precipitate to the bottom. As this process is very slow, the urine is centrifuged for about 5 minutes at 1500 or 2000 revolutions per second to obtain a sample of the sediment in less time.

Bacteria under the microscope are usually of two different types:

  • Bacilli: Rod shape
  • Cocci: Spherical shape

Which does an abnormal result mean?

Bacteria is reported as few, moderate, or many per high-power-field , but a quantitative system of 1+ , 2+, or 3+ may be used.

When bacteria are present in the urine specimen in high numbers and white blood cells (WBCs) are evident, it may be due to the following reasons:

  • Lower UTI (Urinary Tract Infection).
    • Cystitis
    • Urethritis
    • Prostatitis
  • Upper UTI (Urinary Tract Infection).
    • Pyelonephritis
    • Renal or kidney abscess

When bacteria are present in the urine specimen in high numbers and white blood cells are evident, the urinalysis is generally followed up with a culture for positive identification of the bacteria and an antibiotic sensitivity.

The bacteria most frequently associated with UTI (Urinary Tract Infection) are:

  • Enterobacterias (bacilos gram-negativos)
  • Staphylococcus
  • Enterococcus

The most frequent bacterium present in the urine is Escherichia coli, a gram-negative bacterium of the Enterobacteriaceae family.

What other urine test may be affected?

The presence of bacteria in the urine (for example Enterobacteriaceae), may produce a positive nitrite urine test and an alkaline urine (A pH above 8).

Medically reviewed by our Medical staff on 23-09-2021

Bibliography

  • Essentials of Medical Laboratory Practice. Constance L. Lieseke, Elizabeth A. Zeibig. 2012. ISBN: 978-0-8036-1899-2 Pag: 446.
  • Urianalysis and Body Fluids. 5th edition. Susan King Strasinge. Marjorie Schaub Di Lorenzo. 2008. ISBN 978-0-8036-1697-4 Pag 100

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