Pleural SC5b-9 in Differential Diagnosis of Tuberculous, Malignant, and Other Effusions

A monoclonal antibody against soluble phase-terminal complement complex (SC5b-9) was used to try to differentiate pleural effusions of tuberculous vs malignant and other origin. Effusions of tuberculous origin showed a significantly higher SC5b-9 level than did plasma, suggesting activation of complement in the pleural space. All 26 patients with tuberculous effusions showed SC5b-9 levels in pleural fluid exceeding 2.0 mg/L, while 20 with malignant effusions had levels less than 2.0 mg/L. However, rheumatoid, some parapneumonic, and treated malignant effusions showed SC5b-9 levels above 2.0 mg/L. Considering a value exceeding 2.0 mg/L, the specificity and sensitivity of the SC5b-9 estimation in tuberculosis were 0.74 and 1.0, respectively. The mean values for C4d and Bb fragments of complement were significantly (p