From the Guidelines
A pleural effusion is classified as an exudate if it meets at least one of the following Light's criteria: 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 most recent European Respiratory Journal study 1. To differentiate between exudative and transudative pleural effusions, Light's criteria are utilized. 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 If any of these criteria are met, the effusion is classified as exudative; otherwise, it is classified as transudative. This distinction is crucial in clinical practice, as exudative effusions often result from local inflammatory processes, while transudative effusions occur due to systemic factors, according to the British Thoracic Society guideline for pleural disease 1. However, the most recent and highest quality study, published in the European Respiratory Journal in 2024, takes precedence in guiding clinical decision-making 1.
From the Research
Lites Criteria for Pleural Effusion
- Lites criteria are used to determine whether a patient has a transudative or exudative pleural effusion by measuring the concentrations of protein and lactate dehydrogenase (LDH) in the pleural fluid and serum 2.
- The criteria include:
- Pleural fluid/serum protein ratio > 0.5
- Pleural fluid LDH > 2/3 of the upper normal limit in serum
- Pleural fluid/serum LDH ratio > 0.6
- These criteria are useful in distinguishing between transudative and exudative pleural effusions, but may not be perfect and can be influenced by factors such as diuretic therapy 3.
Diagnostic Value of Lites Criteria
- Lites criteria have been shown to have high sensitivity (98%) in detecting exudative pleural effusions, but may not be as effective in ruling out transudates 4.
- The accuracy of Lites criteria has been compared to other biochemical criteria, such as the serum-effusion albumin gradient (SEAG) method, and pleural effusion glucose levels 4, 5.
- Studies have found that Lites criteria are significantly superior to clinical presumption in separating pleural transudates from exudates, but may lose accuracy in patients receiving diuretics 3.
Limitations and Modifications of Lites Criteria
- Lites criteria may not be perfect and can be influenced by factors such as diuretic therapy, which can lead to misclassification of transudates as exudates 3.
- Alternative biochemical criteria, such as the SEAG method, have been proposed as potential alternatives or complements to Lites criteria 4, 5.
- Studies have investigated the use of different cutoff levels for Lites criteria, but have found that modifying the criteria does not offer significant advantages in discriminating between transudative and exudative pleural effusions 6.