<unk>  effusion may be classified according to composition of<unk>  fluid by Light's criteria into two subtypes: exudate and transudate. An increase in plasma osmotic pressure or elevated systemic or pulmonary hydrostatic pressure are alterations that lead to the formation of transudate. In contrast, an exudate results from inflammation and infectious disease of the<unk>  surface, as seen in tuberculosis and pneumonia with effusion, or other disease of the<unk>  surface as seen in malignancy, pancreatitis, pulmonary infarction, or systemic lupus erythematosus.
Light's criteria classifies<unk>  fluid as an exudate if at least one of the following three criteria are fulfilled:<unk>  fluid protein/serum protein ratio greater than 0.5, or<unk>  fluid LDH /serumLDH  ratio greater than 0.6, or<unk>  fluid LDH greater than two-thirds the upper limit of the laboratory's normal serum LDH<unk>  effusion may also be classified according to the appearance of<unk>  fluid, and etiology of the<unk>  fluid:
Serous fluid: hydrothorax
Blood: hemothorax
Chyle: chylothorax
Pus: pyothorax or empyema
Pleural effusion classification
Pneumothorax classification
Hemothorax classification
Pleural empyema classification
Pneumomediastinum classification
Pulmonary edema classification
Hemoptysis classification
Pleural effusion laboratory findings