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Scientific Calendar April 2018

Leucocyte esterase (LE) is one of the standard tests on urine test strips and together with Nitrite (NIT) used for screening for urinary tract infection (UTI).

Which types of white blood cells (WBC) can you detect with this reaction?

1. Eosinophils

2. Neutrophils

3. Lymphocytes

4. Macrophages

5. Basophils

1 and 2

Only 2

All of them

1, 2 and 5

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Scientific background information

Leucocyte esterase is an enzyme exclusively produced by granulocytes and belongs to the group of hydrolases (EC 3)1. This means that urine test strips can exclusively detect neutrophils, eosinophils and basophils.

Under physiological conditions, there are only few WBC found in urine, whereas elevated numbers indicate infection or inflammation of the urogenital tract. The most frequent type of WBC found in urine are neutrophils in the course of urinary tract infections. Apart from bacterial, also non-bacterial disorders such as glomerulonephritis or lupus nephritis go along with high numbers of leucocytes in urine. The presence of eosinophils is associated with interstitial nephritis²; basophils in urine are mentioned only rarely in the literature³. Mononuclear cells such as lymphocytes are difficult to identify by sediment analysis and not covered by test strip testing. These cells appear in the urinary sediment in the early stages of renal transplant rejections, so it is desirable to detect them from a clinical perspective. The method of choice is cytology analysis after staining.

With regard to UTI screening, parameters and tests excluding UTI with high reliability, i.e. a high negative predictive value (NPV), are required. When compared to urine culture4 as the reference, it should be considered that test strip testing is quick and convenient but inferior to flow cytometric urine particle analysis.

References

1. Webb EC (1992): Enzyme nomenclature 1992: recommendations of the Nomenclature Committee of the International Union of Biochemistry and Molecular Biology on the nomenclature and classification of enzymes. San Diego: International Union of Biochemistry and Molecular Biology by Academic Press. ISBN 0-12-227164-5.
2. King Strasinger S et al. (2008): Urinalysis and Body Fluids. Fifth Edition. ©2008 F. A. Davis Co., Philadelphia.
3. Taylor CA et al. (1990): Basophiluria in acute renal failure: an electron microscopy study of urinary sediment. Am J Kidney Dis. 16(3):266-267.
4. Yusuf E et al. (2017): Performance of urinalysis tests and their ability in predicting results of urine cultures: a comparison between automated test strip analyser and flow cytometry in various subpopulations and types of samples. J Clin Pathol. 70(7):631-636.

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