Rapid diagnosis of infectious pleural effusions by use of reagent strips.

Reagent strips have not yet been tested for use in the diagnosis of infectious pleural effusions. A reagent strip was used to evaluate 82 patients with pleural effusions: 20 patients had transudative effusions, 35 had infectious exudative effusions (empyema in 14 and parapneumonic effusion in 21), and 27 had noninfectious exudative effusions. Pleural fluid protein, as evaluated by the reagent strip, proved accurate for the detection of exudative effusions (sensitivity, 93.1%; specificity, 50%; positive predictive value, 84.3%; negative predictive value, 71.5%; odds ratio [OR], 6.77; and 95% confidence interval [CI], 1.87-24). The reagent strip leukocyte esterase test effectively detected infectious exudative effusions (sensitivity, 42.8%; specificity, 91.3%; positive predictive value, 88.2%; negative predictive value, 51.2%; OR, 4.46; and 95% CI, 1.2-16.4). Pleural pH was significantly predicted by the reagent strip but was of no assistance in categorization of exudative effusions as infectious or noninfectious. Compared with physical, laboratory, and microbiological data, the reagent strip was as accurate for estimation of percentages of infectious and noninfectious exudative effusions. Thus, reagent strips may be a rapid, easy-to-use, and inexpensive technique for discriminating transudative from exudative pleural effusions and for categorizing exudative pleural effusions as infectious or noninfectious.