What are Light's criteria?

From the Guidelines

Light's criteria should be used to classify a pleural effusion as an exudate if it meets any one of the following thresholds: pleural fluid to serum protein ratio greater than 0.5, pleural fluid to serum LDH ratio greater than 0.6, or pleural fluid LDH greater than two-thirds the upper limit of normal for serum LDH, as stated in the 2024 European Respiratory Journal study 1. To apply these criteria, the following parameters and thresholds should be considered:

• Pleural fluid to serum protein ratio: the ratio should be greater than 0.5 to indicate an exudate
• Pleural fluid to serum LDH ratio: a ratio greater than 0.6 suggests an exudative effusion
• Pleural fluid LDH: values greater than two-thirds the upper limit of normal for serum LDH are indicative of an exudate These criteria are essential in differentiating between exudative and transudative pleural effusions, as the underlying causes and management strategies differ significantly between the two types. Key points to consider when using Light's criteria include:
• The high sensitivity of the criteria for identifying exudates, which is around 98% 1
• Potential misclassification of transudates in patients on diuretics, which may require additional tests like calculating the serum-pleural albumin gradient to ensure accurate classification
• The importance of proper differentiation between exudates and transudates to guide appropriate diagnostic workup and treatment, as exudates often result from local processes such as infections or malignancies, while transudates are typically caused by systemic conditions like heart failure or cirrhosis.

From the Research

Light's Criteria

Light's criteria are used to differentiate transudative from exudative pleural effusions. The criteria include:

• Pleural fluid protein to serum protein ratio greater than 0.5
• Pleural fluid LDH to serum LDH ratio greater than 0.6
• Pleural fluid LDH greater than two-thirds the upper limit of normal for serum LDH 2, 3, 4, 5, 6

Diagnostic Properties

The diagnostic properties of Light's criteria have been compared to those of several other analytes for the classification of pleural fluids into transudative and exudative.

• The accuracy of Light's criteria was found to be 93% in one study 2
• The sensitivity and specificity of Light's criteria were found to be 100% and 73%, respectively, in one study 2
• The accuracy of Light's criteria was found to be 87.87% in another study, which was lower than the diagnostic accuracy of serum effusion albumin gradient (SEAG) (92.42%) 4

Limitations

There are some limitations to Light's criteria, including:

• The criteria may misclassify about 25% of transudates as exudates, particularly in patients on diuretics 3
• The accuracy of Light's criteria may be lower in patients receiving diuretic therapy, with an accuracy of 83% in one study 5
• Changing the classic Light's criteria with different cutoff points may not offer any advantages for discriminating between transudative and exudative pleural effusions 6

Comparison to Other Criteria

Light's criteria have been compared to other criteria, including:

• Serum-pleural fluid albumin and protein gradients, which had lower accuracy than Light's criteria in one study 5
• SEAG, which had higher diagnostic accuracy than Light's criteria in one study 4
• Combination of pleural cholesterol concentration and effusion LDH activity, which had higher discriminatory potential than Light's criteria in one study 2