LEUKOCYTE ESTERASE IN URINE

LEUKOCYTE ESTERASE

The azurophilic or primary granules of granulocytes, mainly neutrophils, demonstrate esterase activity. Therefore, detection of esterase activity in urine provides an indirect evidence of the presence of leukocytes in urine which is indicative of urinary tract infection. 

The test is more useful when intact leukocytes are not visible microscopically after their disintegration due to phagocytic activity. The leukocyte esterase test is positive with both lysed and intact leukocytes. Reagent strip tests for leukocyte esterase 

Principle:- The test area contains an ester which is hydrolysed by leukocyte esterase to form an alcohol. The aromatic ring in the alcohol molecule reacts with a diazonium salt to form a purple azo dye. The bacteria and red cells in the urine do not affect the reaction. Multistix reagent strips The ester used in this strip is a derivative of a pyrrole amino acid ester. A positive reaction is indicated by a purple colour of the azo dye. About 5-15 leucocytes/hpf should be present in the urine to give a positive test. 

Chemstrip reagent strips:- The ester used in this strip is indoxylcarbonic acid ester, which forms a purple compound in the presence of leukocyte esterase and a diazonium salt. At least 10 leucocytes/ul should be present for a visible positive reaction.

Clinical Significance

Detectable amount of leukocyte esterase indicates increased number of leukocytes in urine. It is indicative of bacterial infection. In the absence of bacteria, other inflammatory conditions without bacterial infection, treatment with antibiotics, or infections with organisms such as chlamydia may be suspected.