Leukocyte Esterase


Introduction

A urinalysis is routinely done to identify the components of the urine. The presence of leukocyte esterase in the urine is considered to not normal and indicates a pathological condition the individual is experiencing. When the result of the urinalysis is partnered with the symptoms the individual is going through, it is enough to establish a diagnosis [1].leukocyte-esterase

What is leukocyte esterase?

The leukocyte esterase is an enzyme that is released by white blood cells (WBCs). Although it is fairly common to have a few WBC in the urine, this will not produce a positive leukocyte esterase test. Any condition that will significantly increase the number of WBCs in the urine will yield a positive result [1, 2, 3].

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Leukocyte Esterase Urine Test

In a leukocyte esterase urine test, a clean-catch urine sample is the specimen of choice. This method is preferred because contamination of the sample is prevented. It would be ideal to use the urine that has been in the bladder for 2-3 hours. A special kit is used to get the sample and it includes a sterile cup and some sterile wipes. It is essential to follow the instructions of the kit to maintain the sterility of the sample [4, 5].

urine-leukocyte-esterase

For men, the head of the penis is cleaned by the provided sterile wipe. If he is uncircumcised, the foreskin must be retracted first. For women, the inner folds of the labia and the urethra should be cleaned using the wipes. The labia must be spread open while urinating.

The person must urinate a small amount into the toilet bowl and then he or she must stop the flow the urine. The sterile urine cup should be held a few inches away from the urethra and must be filled halfway. After getting the recommended amount, the person can continue urinating in the toilet bowl [4, 5].

The medical professional will dip a test strip into the urine sample and one of the color blocks in the strip will change color depending on the amount of leukocytes in the urine. The dipstick test should be done right away because using a stale sample may give a different result.[4, 5]

Clinical Significance

A positive leukocyte esterase result means there is pyuria or an increased amount of leukocytes in the urine. This result means that the individual may have a urinary tract infection. Pathologic conditions such as urethritis and cystitis are also common causes of pyuria.

Sexually transmitted infections (STIs) such as gonorrhea and chlamydia may also increase the WBC in the urine. Further diagnostic tests may be requested following a positive leukocyte esterase result.

A urine culture may be performed in order to identify the pathogen that is causing the infection. It may be accompanied by a pathogen susceptibility test to identify the most appropriate antibacterial drug. It is crucial to finish the entire course of treatment to prevent the reoccurrence of the infection [5, 6].

There may be instances that the urine culture that follows a positive leukocyte result will fail to produce a positive result. A urine culture with no growth after 24 or 48 hours does not always mean that there is no existing infection, it may also mean that the pathogen is not usually picked up by a standard urine culture.

The culture may be repeated in order to look for the bacteria at a lower colony count. STIs such as chlamydia and gonorrhea are also known to produce a negative culture result [5, 6].

A falsely elevated result may occur if the urine sample is contaminated and this finding will be identified after performing a urine culture. There will be different types of bacteria that will grow in the culture and may include nonpathologic bacteria.

The physician may ask to obtain another clean-catch urine sample that is obtained more carefully to identify the infecting bacteria. Following the instructions in the clean-catch kit is essential to avoid contaminating the sample and getting a false-positive result [6, 7].

False-negative results can occur when there is a high amount of protein or glucose. The resulting increase in the specific gravity of the urine will cause the WBC to shrink and not produce the enzyme esterase. If symptoms of infection are present but the esterase result is negative, other tests such as a microscopic count of WBCs will establish the diagnosis of UTI [7].

References

  1. (2014, September 9). Urine Test. Retrieved from WebMD: http://www.webmd.com/a-to-z-guides/urine-test
  2. (2015). Urinary Nitrites and Leukocyte Esterase. Retrieved from RNceus: http://www.rnceus.com/ua/uanile.html
  3. Labtests Online. (2015). Retrieved from Labtests Online: https://labtestsonline.org/understanding/analytes/urinalysis/ui-exams/start/1#nitrite
  4. Health Guide. (2013, August 18). Leukocyte Esterase Urine Test. Retrieved from New York Times: http://www.nytimes.com/health/guides/test/leukocyte-esterase/overview.html
  5. Vorvick, L. (2016, March 2). Clean catch urine sample. Retrieved from Medline Plus: https://www.nlm.nih.gov/medlineplus/ency/article/007487.htm
  6. Labtests Online. (2016, February 16). Urine Culture. Retrieved from Labtests Online: https://labtestsonline.org/understanding/analytes/urine-culture/tab/test/
  7. Coppolino, L. (2015). Chemical Screening of Urine by Reagent Strip. Retrieved from LabCE: https://www.labce.com/spg506387_false_positive_and_negative_urine_leukocyte_estera.aspx

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