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 fundame ntal when investigating the cause of pleural effusions. Acute-phase protein s could be potentially useful markers in this discrimination. Objective: Th e present study was designed to evaluate whether the acute-phase proteins: alpha(2)-macroglobulin (AMG), alpha(1)-acid glycoprotein (AAG) and C-reacti ve 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 us ing 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, respective ly). An AAG value >63 mg/dl in a pleural effusion is predictive of an exuda te 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 sensiti vity and a specificity of 90% and 60%, respectively. Moreover, pleural AAG was significantly higher in cancerous exudates than in exudates and transud ates of all other cause taken together (p < 0.001). Finally, to differentia te 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. Conclusi ons: We conclude that both AAG and AMG concentrations in pleural effusions have a high sensitivity and are therefore useful parameters in distinguishi ng exudates from transudates, but the latter is inferior due to its unaccep tably low specificity. Copyright (C) 2000 S. Karger AG, Basel.