Background: Polymorphonuclear elastase (PMN-E) is a neutrophilic marker that has been implicated in acute inflammatory responses. Objectives: To evaluate the accuracy of PMN-E in the diagnosis of complicated pyogenic effusions. Patients and Method: We studied 536 patients with pleural effusion of various etiologies. There were 125 pyogenic bacterial effusions (42 typical parapneumonic, 17 borderline complicated parapneumonic and 66 complicated parapneumonic or empyema), 83 tuberculous, 91 malignant, 42 paramalignant, 95 transudates, 28 miscellaneous and 72 effusions of unknown origin. Classic markers (pH, glucose, proteins, adenosine deaminase, LDH, leukocytes and differential count) and the PMN-E level were quantified in pleural fluid. The accuracy of PMN-E as an early marker in the diagnosis of complicated pyogenic infectious effusions was evaluated among pleural effusions that were not diagnosed with classic biochemical markers, radiological findings or Gram stain. Since results of pleural fluid culture and cytological examination are generally available after a 48-hour delay, they were not included as early markers in the initial diagnosis of pleural effusions. Results: Early diagnosis of complicated pyogenic bacterial effusions was achieved in only 48 of 66 cases with classic markers. Among those that were not diagnosed with these parameters, a pleural PMN-E value >3,500 µg/l discriminated between complicated and noncomplicated pyogenic bacterial effusions with a sensitivity of 67% and a specificity of 97%. Conclusions: PMN-E is useful in the early diagnosis and management of complicated pyogenic infectious effusions, which may be delayed with classic markers.

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