Significance of alpha-2-macroglobulin, alpha-1-acid glycoprotein, and C-reactive protein in pleural effusion differentiation

Background: The differentiation between exudates and transudates is fundamental when investigating the cause of pleural effusions. Acute-phase proteins could be potentially useful markers in this discrimination. Objective: The present study was designed to evaluate whether the acute-phase proteins: alpha(2)-macroglobulin (AMG), alpha(1)-acid glycoprotein (AAG) and C-reactive protein (CRP) are useful in investigating the pleural effusions. Methods:We prospectively measured the concentrations of the above proteins in the serum and pleural fluid of 84 consecutive patients with various diseases using a nephelometric assay. Results: Pleural effusion AMG, AAG and CRP were all significantly elevated in the group of patients with exudates compared to patients with transudates (p < 0.001, p < 0.001 and p < 0.01, respectively). An AAG value >63 mg/dl in a pleural effusion is predictive of an exudate with a sensitivity of 90% and a specificity 85%. Similarly, an AMG value >44 mg/dl in a pleural effusion is predictive of an exudate with a sensitivity and a specificity of 90% and 60%, respectively. Moreover, pleural AAG was significantly higher in cancerous exudates than in exudates and transudates of all other cause taken together (p < 0.001). Finally, to differentiate the same pleural effusion, the cut-off value of 1.0 mg/dl of pleural CRP has a sensitivity and a specificity of 74% and 74%, respectively. Conclusions: We conclude that both AAG and AMG concentrations in pleural effusions have a high sensitivity and are therefore useful parameters in distinguishing exudates from transudates, but the latter is inferior due to its unacceptably low specificity. Copyright (C) 2000 S. Karger AG, Basel.