Pleural Effusion Light’s Criteria

Light’s criteria explained

The Light’s criteria consists in an evaluation of protein and LDH parameters to see whether at least one of three rules is being met. If so, the sample provided is likely to be a pleural exudate.

The five parameters to be input are described in the table below:

The main limitation of the model is the fact that it does not account for serum and pleural levels of albumin, thus it only reaches a specificity of 83%.

It was found that actually, 25% of determined exudates are in fact transudates.

Interpretation

There are three rules in the Light’s criteria:

1. Pleural fluid protein / Total serum protein >0.5;

2. Pleural fluid LDH / serum LDH >0.6;

3. Pleural fluid LDH > (2/3 x upper limit of normal serum LDH).

The parameters input are checked against the above three rules by performing the necessary determinations. For positive exudative effusion diagnosis, at least one of the three rules should be satisfied.

If so, the next investigations should be: glucose, ADA, cytology, cell count, pH and in some cases culture.

If none of the rules is met, the sample is likely to be a transudate, the other type of pleural effusion.

About the study

The Light criteria was created in 1972 following a study on pleural fluid from 150 patients. The examination consisted in: pleural fluid cell counts, protein levels and lactic dehydrogenase.

The criteria was associated with more than 70% of exudates but in some cases, diagnosis was missed.

The following table introduces the sensitivities and specificities of the various criteria:

Richard W. Light, the creator of the criteria, is a professor in the Division of Allergy, Pulmonary, and Critical Care Medicine at Vanderbilt University School of Medicine.

Pleural exudate vs. transudate

Depending on the type of fluid and the mechanism of entry in the pleural cavity, there is hydrothorax (serous fluid), hemothorax (blood), pyothorax (pus), urinothorax (urine) or chylothorax (chyle).

The characteristics of normal pleural fluid are:

■ Clear ultrafiltrate of plasma from the parietal pleura;

■ Lactate dehydrogenase (LDH) less than 1/2 of plasma;

■ Less than 2% protein content (1 - 2 g/dL);

■ Less than 1000WBC per mm³;

■ pH of 7.60 - 7.64.

There are two types of pleural effusion, differentiated through the levels of lactate dehydrogenase and protein in the pleural fluid:

■ Transudates are defined as pressure filtration without capillary injury;

■ Exudates are defined as inflammatory fluid between the cells.

The table below shows the differences between the two:

Transudative effusions occur due to imbalances between the hydrostatic and oncotic pressure. Most common causes include congestive heart failure and ascites from cirrhosis.

Exudative effusions are caused by bacterial pneumonia, viral infections, pulmonary embolism or malignancy of several types (lung, breast or lymphoma).

Original source

Light RW, Macgregor MI, Luchsinger PC, Ball WC Jr. Pleural effusions: the diagnostic separation of transudates and exudates. Ann Intern Med. 1972; 77(4):507-13.

Validation

Light RW, Erozan YS, Ball WC Jr. Cells in pleural fluid. Their value in differential diagnosis. Arch Intern Med. 1973; 132(6):854-60.

Other references

1. Light RW. Clinical practice. Pleural effusion. N Engl J Med. 2002; 346(25):1971-7.

2. Paramothayan NS, Barron J. New criteria for the differentiation between transudates and exudates. J Clin Pathol. 2002; 55(1): 69–71.

3. Ferreiro L, Toubes ME, Valdés L. Contribution of pleural fluid analysis to the diagnosis of pleural effusion. Med Clin (Barc). 2015; 145(4):171-7.