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

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. 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 + + +. 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%. 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.