Transudates vs. Exudates Pleural Effusion

Jang, Tae Won

Abstract

Pleural effusions are common and of highly diverse etiologies. These effusions can form based on disease of the pleural membranes themselves or of thoracic or abdominal organs. In initial approach, these effusions can be separated as exudates or transudates with Light's criteria. Exudative pleural effusions meet at least one of the following criteria, whereas transudative effusions meet none: pleural fluid protein-to-serum protein ratio of more than 0.5, pleural fluid lactate dehydrogenase (LDH)-to-serum LDH ratio of more than 0.6, and pleural fluid LDH more than two thirds of the upper normal limit for serum. If a patient appears to have clinically a transudative effusion, additional tests can be assessed to verify its transudative etiology. Congestive heart failure and cirrhosis are responsible for almost all transudative pleural effusions. However, it has been determined that the patient has an exudative pleural effusion, one should attempt to determine which of the diseases, remembering that pneumonia, malignancy, and tuberculosis account for the great majority of all exudative pleural effusions. In all patients with undiagnosed exudative pleural effusions, the appearance of the fluid should be noted, and the pleural fluid protein and LDH levels, glucose level, differential cell count, and microbiologic and cytologic studies should be obtained. In selected patients, other tests on the pleural fluid, such as pH, amylase level, antinuclear antibody level, rheumatoid factor level, adenosine deaminase, lipid analysis, and so forth, may be of value.