BAL Neutrophils, Serum Procalcitonin, and C-reactive Protein to Predict Bacterial Infection in the Immunocompromised Host

Background: Bacterial pulmonary infection is a common life-threatening complication in immunocompromised patients. The results of BAL cultures are not immediately available, and their microbiological yield might be limited by empiric antibiotic prescriptions. We evaluated clinical signs and symptoms, leukocyte counts, C-reactive protein (CRP) levels, procalcitonin levels, and BAL fluid neutrophil percentages as potential markers for bacterial infection in a cohort of immunocompromised patients with pulmonary complications.

Methods: One hundred seven consecutive patients who had been referred for bronchoscopy due to suspected pulmonary infection were included in this study. Based on clinical, laboratory, radiologic, microbiological, and histologic results, patients were classified as having proven bacterial infection (n = 27), possible bacterial infection (n = 11), and no bacterial infection (n = 69).

Results: Most common underlying conditions were hematologic malignancy (n = 62) and solid organ transplantation (n = 20). Clinical parameters were similar in patients with and without bacterial infection (difference was not significant). The percentage of BAL fluid neutrophils had the highest area under the curve (0.818; 95% confidence interval [CI], 0.700 to 0.935; p < 0.001), followed by absolute neutrophil counts (0.797; 95% CI, 0.678 to 0.916; p < 0.001), procalcitonin level (0.746; 95% CI, 0.602 to 0.889; p = 0.001), and CRP level (0.688; 95% CI, 0.555 to 0.821; p = 0.015) to predict proven bacterial infection (in opposition to no or possible bacterial infection) in the receiver operating characteristic analysis. Conversely, neither infiltrates (p = 0.123) nor leukocyte counts (p = 0.429) were useful in diagnosing bacterial infection. The percentage of BAL fluid neutrophils and procalcitonin level were independent predictors of bacterial infection in the multivariate regression.

Conclusions: Neutrophil percentage in BAL fluid, procalcitonin level, and CRP level might be potentially useful to differentiate bacterial infection from nonbacterial conditions in immunocompromised hosts with pulmonary complications.