Diagnostic accuracy cf pleural fluid polymorphonuclear elastase in the differentiation between pyogenic bacterial infectious and non-infectious pleural effusions

Background and Objectives: To establish the diagnostic accuracy of the markers of neutrophil activity (elastase and lysozyme) determined in pleural fluid, for differentiating between pyogenic bacterial infectious and noninfectious pleural effusions. Patients and Methods: At our tertiary referral teaching hospital, 160 patients over 14 years with pleural effusion (PE), classified as pyogenic bacterial infectious (41 parapneumonic complicated, 32 parapneumonic non-complicated) and non-infectious (32 neoplasm and 55 undiagnosed pleural exudates) were examined in a prospective study. Polymorphonuclear elastase (PMN-E) was determined by an immunoactivation method and lysozyme by a turbidimetric method. Receiver operating characteristic (ROC) curves were used to evaluate diagnostic accuracy. Results: Pleural fluid PMN-E was the biochemical marker that best differentiated between pyogenic bacterial infectious and non-infectious PE, The ROC area under the curve (AUC) for PMN-E was 0.8276. A PMN-E value over 230 mu g/l diagnosed infectious PE with a specificity of 0.81 and a sensitivity of 0.74. The ROC AUC for proteins plus lactate dehydrogenase was 0.7430. Differences between the two ROC curves were significant (p = 0.032). After excluding purulent parapneumonic complicated PE, the sensitivity of a pleural fluid PMN-E value equal to or greater than 230 mu g/l was 0.64 and the specificity 0.81. Conclusions: Pleural fluid PMN-E was the marker that best differentiated infectious from non-infectious PE, and PMN-E values lower than 230 mu g/l suggest non-infectious PE. Copyright (C) 2000 S. Karger AG, Basel.