De Light Criteria: Definition, Benefits, Tests, Studies and Results

The first step in evaluating patients with pleural effusion is to determine whether the effusion 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 to better classify the occasional transudate 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 effusion, attempts should be made to define the etiology.

Most exudative effluvia are pneumonia , cancer, tuberculosis, and pulmonary embolism. Many pleural fluid tests are useful in the differential diagnosis of exudative effusions. Other useful diagnostic tests include helical computed tomography and thoracoscopy.

Changing the classic Light criteria with different cut-off points does not offer advantages to discriminate 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.

If 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, 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 clearly 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 rate of misclassification 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 in comparison with the albumin and protein gradients in patients with poorly categorized hepatic hydrothorax (77% vs 62% vs 61%).

The simplest strategy to reveal the true transudative nature of effusions related to heart failure, labeled exudates according to Light’s criteria, 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:

  1. The ratio between pleural fluid protein and serum protein is greater than 0.5.
  2. The ratio of pleural fluid lactate dehydrogenase (LDH) to serum lactate dehydrogenase is greater than 0.6.
  3. The level of lactate dehydrogenase in pleural fluid is greater 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.

If 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, the serum pleural fluid protein gradient should be examined.

In clinical practice, exudative effluvia can be effectively separated from transudative effluvia using Light’s criteria. 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 ratio of pleural fluid lactate dehydrogenase (LDH) to serum lactate dehydrogenase is greater than 0.6.

The level of lactate dehydrogenase in pleural fluid is greater than two-thirds of the upper limit of normal for serum lactate dehydrogenase.

Light’s criteria are nearly 100 percent sensitive for identifying exudates, but approximately 20 percent of patients with pleural effusion caused by heart failure may meet the criteria for an exudative effusion after receiving diuretics.

In these circumstances, if the difference between the protein levels in the serum and the pleural fluid is greater than 3.1 g per dL, the patient should be classified as having a transudative effusion.

A serum albumin effusion gradient greater than 1.2 g per dL may also indicate that the pleural effusion is probably a true transudative effusion.

However, neither protein nor albumin gradients alone should be the primary test used to distinguish transudative effusions from exudative effusions because they result in misclassification of a significant number of exudates.

This lower sensitivity may be caused by the fact that a single test is used as opposed to the combination of three tests from the standard criteria described above.