Use of acute phase proteins in pleural effusion discrimination

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. In the attempt to define diagnostic criteria for the differentiation of pleural exudates from transudates, we measured alpha 1 acid glycoprotein, C-reactive protein, haptoglobin, ceruloplasmin and transferrin in pleural effusions and serum in patients with pleural effusions of various etiologoies. We measured the concentrations of the above proteins in the serum and pleural fluid of 80 (54 exudate, 26 transudate) consecutive patients by immunoturbidometrical methods. Pleural effusion acute phase proteins were elevated in the patients with exudate compared to patients with transudate (p< 0.001 for all). In receiver operator characteristic analysis showed that pleural fluid ceruloplasmin levels and the ratio pleural fluid/serum transferrin were superior to the others. Using the optimum cut-off point of 0.16 g/L pleural fluid ceruloplasmin achieves a sensitivity of 92% with a specificity of 85%. In addition to, the optimum cut-off point for pleural fluid/serum transferrin ratio was 0.4 with sensitivity and specificity of 92% and 80%. When using together these parameters sensitivity and specificity were increased (95%, 85%). In differential diagnosis, none of these proteins were significantly different in subgroups of pleural exudate. We conclude that when using together ceruloplasmin levels in pleural fluid and the ratio of pleural to serum transferrin have a high sensitivity and specificity in discrimination of exudative pleural effusions.