Light's Criteria OR transudate vs exudate

Light's Criteria

Determination of transudate versus exudate source of pleural effusion

Fluid is exudate if one or more of the following Light’s criteria is present:^{[1, 2, 3, 4]}

Mnemonic: 5,6,7 PLR. (Like "pleura"):

• Effusion protein/serum protein ratio greater than 0.5
• Effusion lactate dehydrogenase (LDH)/serum LDH ratio greater than 0.6
• Effusion LDH level greater than two-thirds (0.67) the upper limit of the laboratory's Reference range of serum LDH

Exudative effusions

See the list below:

• Abdominal abscess fluid near lung or PNA, Meigs syndrome (ovarian tumor, ascites, pleural effusion), pancreatitis
• Connective-tissue disease: Churg-Strauss disease, lupus, rheumatoid arthritis, Wegener granulomatosis
• Endocrine: Hypothyroidism, ovarian hyperstimulation
• Iatrogenic: Drug-induced, esophageal perforation, feeding tube in lung
• Infectious: bacterial pneumonia, fungal disease, parasites, tuberculosis
• Inflammatory: Acute respiratory distress syndrome (ARDS), asbestosis, pancreatitis, radiation, sarcoidosis, uremia
• Lymphatic abnormalities: Chylothorax, malignancy, lymphangiectasia
• Malignancy: Carcinoma, lymphoma, leukemia, mesothelioma, paraproteinemia

Transudative effusions

See the list below:

• Atelectasis: Due to increased negative intrapleural pressure
• Cerebrospinal fluid (CSF) leak into pleural space: Thoracic spine injury, ventriculoperitoneal (VP) shunt dysfunction
• Heart failure
• Hepatic hydrothorax
• Hypoalbuminemia
• Iatrogenic: Misplaced catheter into lung
• Nephrotic syndrome
• Peritoneal dialysis
• Urinothorax: Due to obstructive uropathy

Exceptions

These are processes that typically cause exudative effusions, but may cause transudative effusions.

• Amyloidosis
• Chylothorax
• Constrictive pericarditis
• Hypothyroid pleural effusion
• Malignancy
• Pulmonary embolism
• Sarcoidosis
• Superior vena cava obstruction
• Trapped lung