Light’s Criteria for Exudative Effusions
Why Use
Calculation of Light’s criteria provides a systematic, validated approach to evaluating pleural fluid studies. It can save the clinician significant time and avoid unnecessary additional workup. Remember, however, that Light’s criteria is more sensitive than specific test for exudative effusions.
When to Use
Light’s criteria can be used to determine the type of a patient’s pleural effusion and thus its etiology.
Formula
Pearls / Pitfalls
The following diseases typically are exudative effusions, but in certain cases may be transudative: Amyloidosis Chylothorax Constrictive pericarditis Malignancy Pulmonary embolism Sarcoidosis Trapped lung Light’s criteria are more sensitive than specific for exudative effusions.
Management
Perform a diagnostic and therapeutic needle thoracentesis or chest tube drainage of pleural effusion. Obtain pleural fluid and serum studies of protein and LDH. Consider additional pleural fluid studies (cell count, differential, culture, cytology, triglycerides). Determine if pleural fluid is exudative by meeting at least one of Light’s criteria: Pleural fluid protein / Serum protein >0.5 Pleural fluid LDH / Serum LDH >0.6 Pleural fluid LDH > 2/3 * Serum LDH Upper Limit of Normal Review table 1 below to narrow differential: Exudative Transudative Malignancy Heart failure ARDS Atelectasis Meigs syndrome CSF leak into pleural space Pancreatitis Hepatic hydrothorax Eosinophilic granulomatosis with polyangiitis Hypoalbuminemia Granulomatosis with polyangiitis Nephrotic syndrome Lupus Peritoneal dialysis Lung abscess Urinothorax Chylothorax Sarcoidosis Hypothyroidism Fluid color itself can also assist in suggesting a potential etiology as in table 2: Fluid Appearance/Odor Necessary Fluid Study Differential Bloody Hematocrit and RBC count Malignancy, trauma, PE, hemothorax Cloudy Triglycerides Chylothorax Putrid odor Gram stain and culture Anaerobic infection
Critical Actions
Proper diagnosis of the underlying etiology is important as the treatments for the numerous exudative and transudative etiologies differ significantly. Typically, exudative effusions require a further investigative workup which may include cytopathology studies, biopsy, or even a thoracotomy. Conversely, transudative effusions usually resolve with treatment of the underlying condition.
Advice
A thoracentesis is typically indicated if a clinically significant pleural effusion is present that is radiographically at least 10mm thick. A transudative effusion occurs due to an imbalance between the hydrostatic and oncotic pressure. An exudative effusion, however, represents an alteration of the local factors that then precipitates a pleural fluid accumulation.
More Information
Note : While Light’s Criteria are reported to be highly sensitive for exudative effusions, their specificity for exudative effusions is only 83%. Please see table 3 to compare sensitivities and specificities of the various criteria. Light’s Criteria Sensitivity (%) Specificity (%) Light’s Criteria (1 or more of the following 98 83 Pleural fluid protein / Serum protein >0.5 86 84 Pleural fluid LDH / Serum LDH >0.6 90 82 Pleural fluid LDH > 2/3 * Serum LDH upper limit of normal 82 89