Correlation of leukocyte esterase detection by reagent strips and the presence of neutrophils: a study in BAL fluid

Study objective: In the present study, we evaluated the leukocyte esterase (LE) area of a reagent strip designed for urinalysis for the semiquantitative measurement of the percentage of polymorphonuclear neutrophils (PMNs) in BAL fluid. Design: Prospective, The relative PMN counts (obtained by conventional microscopy and expressed as a percentage of a 500 cell count) of consecutive BAL fluid samples were compared with the corresponding LE categories as read with a urine chemistry reader. LE categories were graded as follows: negative, trace, +, + +, and + + +. Results: A total of 153 BAL fluid samples were included. The mean PMN counts of the negative LE category (4.1 +/- 4.3%; n = 43) and the + + + category (81.8 +/- 16.3%; n =37) differed significantly from each other and from the mean PMN counts of the other categories. Within the trace, +, and + + categories, a considerable overlap of PMN counts was noted. Assignment of a BAL fluid to the negative LE category consistently predicted a PMN count <20%. At a threshold value of 50% PMNs, the + + + LE category predicted the BAL fluid samples to the correct group (PMNs > 50% vs <50%) with a sensitivity of 70.8% and a specificity of 97.1%. Conclusions: The reagent strips proved to be useful as a rapid test for semiquantitative measurement of the relative PMN counts in BAL fluid. However, the low predictive value for the exclusion of a high PMN count may limit their application.