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.