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Leukocyte Esterase

Last reviewed by Dr. Raj MD on January 12th, 2022.

What is Leukocyte Esterase

Leukocyte esterase is an enzyme which can be found in urine or feces. It simply shows evidence of infection and/or inflammation.

In this article, you will learn why it is a necessary exam, what it represents, how the results are shared and how it is performed.

Next we will be discussing briefly the life cycle of a white blood cell in order to give the foundation for the topic.

Life of a White Blood Cell

Image 1 : Life cycle of a white blood cell
Picture Source : www.cancer.gov

The process is as follows:

  1. All blood cells originate as blood stem cells.
    b.    Those that grow into lymphoid stem cells grow into lymphoblasts, these lymphoblasts create the three most commonly known white blood cells (B lymphocytes, T lymphocyte, and natural killer cell).
    c.    On the other hand, those that grow into myeloid stem cells may then transform into myeloblasts creating granulocytes. There are three forms of granulocytes (eosinophil, basophil, and neutrophil)
    d.    Each type of white blood cell has its function. (4)

What is a Leukocyte?

The proper pronunciation is (LOO-koh-site). A leukocyte is simply the medical term for white blood cells. These cells are made in the bone marrow and transferred throughout the body in the lymph system. Their specific function is to fight against diseases and infection and is highly noted during inflammation processes.

There are various types of leukocytes as explained in Image 1. These types of lymphocytes include granulocytes (eosinophil, neutrophil, and basophil), B and T lymphocytes and monocytes. (1, 4, 5)

What is Esterase?

The proper pronunciation is (es·ter·ase). It is literally an enzyme which increases the production of esters a product of the leukocyte process. (4)

With this foundation of information, we can digest and properly explain the leukocyte esterase trace (LET).

  • It checks for the presence of the specific esterase produced by leukocytes in urine and feces.
  • Can be checked using dip sticks (Picture 2) without the need for lab standard microscopes. They also help to lower the time needed to receive results. This time is lowered to minutes instead of hours. They are easy to use, can be used almost anywhere and are extremely cost effective.  (1,6)
  • Multiple studies have shown the practicality and functionality of the dip sticks for checking for leukocyte esterase. Dip sticks are less costly and easier to use in small lab settings. There have been some false negatives and some false positives in each of these studies but for the most part when practicality is the main issue the dip stick is the method of choice. (1,2,3,5,6)
  • The false negatives noted in studies have been shown to be caused by one of the following:
  • High protein
  • High Vitamin C (1,2,3,5,6,9)

Urine Dipstick
Picture 2: Urine Dipstick
Photo Source : www.newkidscenter.com

What types of diagnosis can be found by checking for Leukocyte Esterase?

  • Above all, it is to look for signs of white blood cells which will prove infection or inflammation. (11)
  • It could be used for acute febrile prostatitis and cystitis in women (3)
  • Studies have tried to prove its ability to check for chlamydia and shown that it is not helpful (1)
  • Can be used to show positive urinary tract infection in male and female patients when using a midstream urine sample. (Midstream urine sample consists of a patient first release a small amount of urine and the dip stick being placed during the continued flow.) (3)

Important notice: It is used as a filter to decide if there is in fact infection. But antibiotics should not be prescribed until the urine has been viewed under a microscope and identified in order to prescribe the correct antibiotic. (11)

Leukocyte Esterase : Normal range (Chart and Analysis)

The basic answer is that negative is normal and positive shows an abnormal range. The strip is dipped into the urine that is to be tested and the change of color is compared with the standard chart in the image below and range is noted.

If numbers such as those noted in the list below are seen it speaks of the color showing on the dipstick (see Figure 3) and the density of the leukocyte esterase in the urine:

  • Leukocyte esterase 1
  • Leukocyte esterase 2
  • Leukocyte esterase 3
  • Leukocyte esterase ua large
  • Leukocyte esterase ua moderate

dipstik test urine Leukocyte esterase
Figure 3 : Various parts of a dip stick.
Photo Source : library.med.utah.edu

What should I expect when being checked for Leukocyte Esterase?

There are two ways to check for leukocyte esterase in the urine, a dip stick, and a urinalysis. A visual exam of the urine may also be part of the routine.

  • The dipstick test is easy and practical. It is usually done by collecting midstream urine on a stick.
  • The patient should understand how to do a midstream urine collection. This is done by waiting for the collection until the patient has released the urine for a few seconds.
  • The patient should also understand how to do a clean catch urine sample which includes the need to clean themselves from front to back before releasing urine. (1,7,9,0,11)
  • Urinalysis
  • As noted above a midstream clean-catch urine sample is needed.
  • This sample will be collected in a sterile cup.
  • Some labs will give you a kit which will have a sanitary wipe in order to wipe (front to back) and the cup. (8,9,10,11)
  • Visual exam: Lab technicians or nurses will also view the urine to be sure there is no presence of other particles.
  • Both exams will be annualized right away and are not considered accurate if much time passes after collection.
  • There is nothing specific that you need to do to prepare for the test although the first urination of the day is always the most accurate. The urine should have been in the bladder for at least four hours for the most accurate outcome. (7,9,10)

Frequently asked Questions:

What is the Significance of a positive Leukocyte Esterase?

A positive leukocyte esterase test basically shows that there is a process of white blood cells in the urine. The evidence of white blood cells in the urine is usually indicative of infection or inflammation.

What is a Leukocyte Esterase test?

Leukocyte esterase test is done with any urinalysis and can be tested using a urine dipstick. The purpose of this test is to check for infection or inflammation.

What are any special considerations for Leukocyte Esterase with pregnancy?

There are no special considerations regarding leukocyte esterase in pregnancy. Although pregnancy does put women at a higher risk for urinary tract infections, therefore, they may see testing being done more frequently while pregnant.


  1. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC228841/pdf/340534.pdf
  2. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1852264/pdf/IDOG-11-019.pdf
  3. https://academic.oup.com/cid/article-lookup/doi/10.1086/528873  Performance of the Urine Leukocyte Esterase and Nitrite Dipstick Test for the Diagnosis of Acute Prostatitis, Manuel Etienne,  Martine Pestel-Caron,  Pascal Chavanet,  François Caron
  4. https://www.cancer.gov/publications/dictionaries/cancer-terms?cdrid=46067 Deffinitions
  5. http://jcm.asm.org/content/21/5/840.long , MICHAEL A. PFALLER AND FRANKLIN P. KOONTZ
  6. http://clinchem.aaccjnls.org/content/clinchem/39/12/2531.full.pdf
  7. https://medlineplus.gov/ency/article/003584.htm Leukocyte esterase urine test
  8. http://www.rnceus.com/ua/uanile.html Urinary Nitrites and Leukocyte Esterase
  9. http://www.mayoclinic.org/tests-procedures/urinalysis/details/results/rsc-20255397 Urinalysis
  10. http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-31802006000300006&lng=en&nrm=iso&tlng=en  Sao Paulo Med. J. vol.124 no.3 São Paulo  2006
  11. https://www.ucsfhealth.org/tests/003584.html
  12. http://library.med.utah.edu/WebPath/TUTORIAL/URINE/URINE.html

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