Light's Criteria for Exudative Pleural Effusion

 

Input
 

Pleural fluid protein		g/L g/dL gm/L gm/dL mcg/dL mcg/mL mg% mg/dL mg/mL ng/mL
Total serum protein		g/L g/dL gm/L gm/dL mcg/dL mcg/mL mg% mg/dL mg/mL ng/mL
Pleural fluid LDH		IU/L IntUnit/L U/L Unit/L Units/L mcKat/L
Serum LDH		IU/L IntUnit/L U/L Unit/L Units/L mcKat/L
Upper limit of normal serum LDH		IU/L IntUnit/L U/L Unit/L Units/L mcKat/L

 
Results
 
Important: Inputs must be complete to perform calculation.

 

Pleural fluid protein to serum protein ratio
Pleural fluid LDH to Serum LDH ratio
Pleural fluid LDH to Upper limit of normal serum LDH ratio
Decimal Precision   0 1 2 3

 

Light's criteria interpretation

 

Criteria for an exudative effusion

Pleural fluid protein to serum protein ratio >0.5

Pleural fluid LDH to serum LDH ratio >0.6

Pleural fluid LDH to upper limit of normal serum LDH >0.66666

Classification

Transudative effusion is likely

Exudative effusion is likely

 

 

 

Notes

• In this calculator, mcg is the abbreviation for micrograms.
• If the ratio of pleural fluid protein to serum protein is >0.5, then an exudate is likely.
• If the ratio of pleural fluid LDH to serum LDH is >0.6, then an exudate is likely.
• If the pleural fluid LDH is greater than two-thirds the upper limit of the laboratory's normal serum LDH, then an exudate is likely.
• LDH: lactate dehydrogenase enzyme activity.

 
Equations used
 

Pleuralfluidproteintoserumproteinratio = Pleuralfluidprotein / Totalserumprotein

PleuralfluidLDHtoSerumLDHratio = PleuralfluidLDH / SerumLDH

PleuralfluidLDHtoUpperlimitofnormalserumLDHratio = PleuralfluidLDH / UpperlimitofnormalserumLDH

 

 

References

1. Light RW, Macgregor MI, Luchsinger PC, Ball WB Jr. Pleural effusions: the diagnostic separation of transudates and exudates. Ann Intern Med. 1972; 77:507.
2. Heffner JE, Brown LK, Barbieri CA. Diagnostic value of tests that discriminate between exudative and transudative pleural effusions. Primary study investigators. Chest. 1997; 111:970.