New dip-and-read test for determining leukocytes in urine

Abstract

A new reagent strip for the determination of leukocytes in urine (LEUKOSTIX; Ames) is described. The test is based on the esterase activity in leukocytes as a marker. Upon contact between the reagent matrix and a urine containing leukocytes, an amino acid ester is hydrolyzed by the esterase to its corresponding alcohol. The free alcohol then couples with a diazonium salt to produce a purple azo dye. The relative concentration of leukocytes in the urine is obtained by visually comparing the strip reaction with a color chart. Performance of the strip was evaluated in a clinical study involving eight different sites and 867 urine specimens. The comparison method was sediment microscopy; specimens containing five cells or more per high-power field were considered to be positive. Sensitivity was 76.3%, specificity 80.8%. Performance was comparable with that of the CHEMSTRIP LN (Boehringer-Mannheim Diagnostics, Inc.) leukocyte test, which we evaluated concurrently.