Diagnostic value of sialic acid in malignant pleural effusions

In this study, we measured pleural fluid and serum sialic acid levels in 70 consecutive patients hospitalized with pleural effusions and serum sialic acid concentrations in 20 healthy individuals chosen as control group. The cause of 26 pleural effusions was malignancy, and diseases other than malignant neoplasms were determined as the cause of 44 cases. Mean serum sialic acid levels in the patients with malignancies were higher than the levels in patients with nonmalignant diseases and the control group. Mean sialic acid level in the patients with nonmalignant diseases was increased compared with control group, but this increase was not as high as that in the patients with malignancies. In the patients with malignant neoplasms, mean pleural fluid sialic acid content was also higher than that found in other diseases. Sialic acid concentration of pleural fluid was correlated with serum concentration. However, pleural fluid to serum sialic acid ratio in malignant diseases was greater than that in the others. The specificity and sensitivity of pleural fluid sialic acid level in excess of 0.075 mg/ml in distinguishing malignant effusions were 68 percent and 77 percent, respectively. These values for pleural fluid/serum sialic acid ratio with the cut-off level of 0.7 were 55 percent and 65 percent. Our findings indicate that determination of sialic acid level in malignant pleural effusions has a diagnostic value.