Pleural SC5b-9: a test for identifying complicated parapneumonic effusions.

BACKGROUND AND OBJECTIVES We have tested whether the complement activation products SC5b-9 and C3a-desArg are useful to distinguish complicated (CPE) from uncomplicated parapneumonic effusions (UPE).

Methods: A total of 66 patients were enrolled in the study: 5 with empyema, 19 with CPE, 12 with UPE, and 30 transudates who served as controls. SC5b-9 and C3a-desArg were measured by commercial ELISA tests, and their performances were evaluated using receiver operating characteristic (ROC) analysis.

Results: Patients with CPE had higher mean levels of pleural SC5b-9 (8,218 microg/l) and C3a-desArg (8,790 microg/l) than those with UPE (2,227 and 3,772 microg/l, respectively; p < 0.0001), whereas concentrations in the latter were comparable with controls for the SC5b-9 test. Empyemas had a wide range of pleural complement activation product values. Pleural SC5b-9 and C3a-desArg showed very high diagnostic accuracy in the diagnosis CPE (90.3 and 77.8%, respectively) when corresponding cutoff points of 2,000 and 4,000 microg/l were used. In a stepwise logistic regression analysis, the combination of SC5b-9 >/=2,000 microg/l, LDH >/=1,000 U/l and a pleural polymorphonuclear percentage >/=85% provided the highest discriminative power for the diagnosis of CPE (area under ROC curve 0.97).

Conclusions: This pilot study suggests that measurement of pleural SC5b-9 can be useful in the workup of patients with a parapneumonic effusion in order to differentiate CPE from UPE.