Accuracy of complement activation product levels to detect infected pleural effusion in rats.

BACKGROUND: Pleural empyema is a well-known complication of pneumonia. If treatment is delayed, empyema may increase morbidity and mortality in affected patients. Therefore, the identification of empyema biomarkers in parapneumonic pleural effusion is desirable. Previous research has suggested complement activation products as candidate empyema markers.

OBJECTIVE: To compare the levels of complement activation products C3a, C5a, and C5b9 in pleural effusion induced by Staphylococcus aureus (SA), Streptococcus pneumoniae (SP), or turpentine (control).

METHODS: Thirty-nine male Wistar rats (mean weight 414 g; 290-546 g) were allocated as follows: 17 animals in the SA group, 12 in the SP group, and 10 in the control group. Bacteria or turpentine were injected into the pleural space. After 12 hr, intrapleural fluid was collected using ultrasound-guided thoracentesis. Levels of complement activation products were determined using ELISA kits.

RESULTS: Two SA and one SP animals died before 12 hr. Mean levels were as follows: C3a: 1066.82 µg/ml (937.29-1196.35 µg/ml) in SA, 1188.28 µg/ml (1095.65-1280.92 µg/ml) in SP, and 679.13 µg/ml (601.29-756.98 µg/ml) in controls (P < 0.001); C5a: 55.727 ng/ml (41.22-70.23 ng/ml) in SA, 520.107 ng/ml (278.92-761.3 ng/ml) in SP, and 5.268 ng/ml (1.68-8.85 ng/ml) in controls (P < 0.001); C5b9: 15.02 ng/ml (13.1-16.94 ng/ml) in SA, 16.63 ng/ml (14.37-18.9 ng/ml) in SP, and 14.05 ng/ml (9.8-18.29 ng/ml) in controls (P = 0.692). ROC analysis revealed an area under the curve of 0.987 (95% CI: 0.953-1) for C3a; 1 (1-1) for C5a; and 0.757 for C5b9 (0.523-0.990).

CONCLUSIONS: In the present rat model, complement activation fragments C3a and C5a accurately detected infected pleural effusion. Pediatr Pulmonol. 2017;52:757-762. © 2017 Wiley Periodicals, Inc.