Differential diagnostic criteria in pleural effusions

Studying the pleural effusion, apart from the information obtained trough clinical presentation, observation, follow-up and elements perceived with the thoracentesis, a certain number of simple and usual laboratory variables can be greatly helpful, not only to distinguish between pleural effusions of transudative or exudative nature, but also to reach a correct differential diagnosis. For these purposes, a relatively small number of tests, properly combined, can assure a correct diagnosis in the large majority of cases. Concerning the chemical analysis of pleufal fluid, particular importance is given to pH and to the concentrations (often compared with the serum ones) of proteins, LDH, glucose and amylase. To the same diagnostic aim, important information is often obtained by the microscopic study of nucleated cells such as neutrophils, lymphocytes, eosinophils, mesothelial cells, in the pleural fluid.