Index
The first step in evaluating patients with pleural effusion is determining whether the flow is transudate or exudate.
Light’s criteria are a common and effective method to differentiate exudates from pleural transudates. An exudative effusion is diagnosed if the patient meets Light’s criteria.
Serum to pleural fluid protein or albumin gradients may help classify the occasional transudate better mistakenly identified as an exudate based on these criteria.
If the patient has a transudative effusion, therapy should be directed toward the underlying heart failure or cirrhosis. If the patient has an exudative flow, attempts should be made to define the etiology.
Most exudative effluvia are pneumonia, cancer, tuberculosis, and pulmonary embolism. Many pleural fluid tests are helpful in the differential diagnosis of exudative effusions. Other functional diagnostic tests include helical computed tomography and thoracoscopy.
Changing the classic Light criteria with different cut-off points does not offer advantages to discriminating between exudative and transudative pleural effusions.
Profits
Light’s criteria serve as a good starting point in separating transudate from exudate. Light’s criteria misclassify about 25% of transudates as exudates, and most of these patients receive diuretics.
Suppose a patient is thought to have a disease that produces a transudative pleural effusion, but Light’s criteria suggest an exudate only by a small margin. In that case, the serum pleural fluid protein gradient should be examined.
Tests
Light’s criteria combine three dichotomous tests into a decision rule that is considered positive if any of the tests are positive.
This strategy maximizes sensitivity, albeit at the expense of specificity. Although Light’s criteria identify 98% of pleural exudates, they misclassify about 25% of transudates as exudates.
Pleural effusions are most commonly due to heart failure (HF) or hepatic hydrothorax (HH), but some of these effusions are erroneously classified as exudates according to Light’s standard criteria.
Traditionally, measurement of the protein gradient between serum and pleural fluid has been recommended to decrease the misclassification rate of Light’s criteria.
Studies
A recent study showed that a gradient between serum albumin levels and pleural fluid of more than 1.2 g / dl has a significantly better performance than a protein gradient of more than 3.1 g / dl to classify correctly—mislabeled heart effusions (83 vs. 55%).
On the other hand, the precision of a pleural albumin index in pleural fluid less than 0.6 stood out compared to the albumin and protein gradients in patients with poorly categorized hepatic hydrothorax (77% vs. 62% vs. 61%).
According to Light’s criteria, the most straightforward strategy to reveal the true transitive nature of effusions related to heart failure, labeled exudates, is to calculate the pleural fluid serum-albumin gradient.
In contrast, for poorly classified hepatic hydrothorax, measurement of the pleural ratio to serum albumin is recommended. The gradient of whey protein to pleural fluid should no longer be considered the preferred test for this purpose.
Consider additional studies on pleural fluid (cell count, differential, culture, cytology, triglycerides).
Exudative pleural effusions meet at least one of the following criteria, while transudative pleural effusions meet none:
- The ratio between pleural fluid protein and serum protein is more significant than 0.5.
- The percentage of pleural fluid lactate dehydrogenase (LDH) to serum lactate dehydrogenase is more critical than 0.6.
- The lactate dehydrogenase level in pleural fluid is more vital than two-thirds of the upper limit of normal for serum lactate dehydrogenase.
Results
Light’s criteria serve as a good starting point in separating transudate from exudate. Light’s criteria misclassify about 25% of transudates as exudates, and most of these patients receive diuretics.
Suppose a patient is thought to have a disease that produces a transudative pleural effusion, but Light’s criteria suggest an exudate only by a small margin. In that case, the serum pleural fluid protein gradient should be examined.
Using Light’s criteria in clinical practice, exudative odors can be effectively separated from transudative effluvia. These criteria classify an effusion as exudate if one or more of the above criteria are present:
The ratio between pleural fluid protein and serum protein is greater than 0.5. The percentage of pleural fluid lactate dehydrogenase (LDH) to serum lactate dehydrogenase is greater than 0.6.
The lactate dehydrogenase level in pleural fluid is more significant than two-thirds of the upper limit of normal for serum lactate dehydrogenase.
Light’s criteria are nearly 100 percent sensitive for identifying exudates. Still, approximately 20 percent of patients with pleural effusion caused by heart failure may meet the requirements for an exudative flow after receiving diuretics.
Suppose the difference between the protein levels in the serum and the pleural fluid is more significant than 3.1 g per dL. In that case, the patient should be classified as having a transudative effusion.
A serum albumin effusion gradient more significant than 1.2 g per dL may also indicate that the pleural effusion is probably a genuine transudative effusion.
However, neither protein nor albumin gradients alone should be the primary test to distinguish transudative effusions from exudative effusions. They result in the misclassification of a significant number of exudates.
