According to Light's criteria, which combination indicates a transudative pleural effusion?

According to Light's criteria, which combination indicates a transudative pleural effusion?

• A. Protein ratio <= 0.5, LDH ratio <= 0.6, pleural LDH <= 2/3 ULN
• B. Protein ratio > 0.5
• C. LDH ratio > 0.6
• D. Pleural LDH > 2/3 ULN

Answer: (A)

Light's criteria distinguish transudates from exudates by three measurements: the pleural fluid to serum protein ratio, the pleural fluid to serum LDH ratio, and the absolute pleural fluid LDH relative to the upper limit of normal for serum LDH. A transudative effusion occurs when none of the exudate thresholds are met, meaning the pleural fluid is low in protein and LDH compared with serum, and the pleural LDH is not elevated above the ULN. The combination described—protein ratio 0.5 or less, LDH ratio 0.6 or less, and pleural LDH not exceeding two-thirds of the ULN—satisfies all three “not exudate” criteria, so it indicates a transudative effusion. In contrast, if any one of those thresholds were exceeded, the effusion would be classified as exudative, pointing to inflammation, infection, malignancy, or other processes that increase vascular permeability or protein leakage.

Light's criteria distinguish transudates from exudates by three measurements: the pleural fluid to serum protein ratio, the pleural fluid to serum LDH ratio, and the absolute pleural fluid LDH relative to the upper limit of normal for serum LDH. A transudative effusion occurs when none of the exudate thresholds are met, meaning the pleural fluid is low in protein and LDH compared with serum, and the pleural LDH is not elevated above the ULN.

The combination described—protein ratio 0.5 or less, LDH ratio 0.6 or less, and pleural LDH not exceeding two-thirds of the ULN—satisfies all three “not exudate” criteria, so it indicates a transudative effusion.

In contrast, if any one of those thresholds were exceeded, the effusion would be classified as exudative, pointing to inflammation, infection, malignancy, or other processes that increase vascular permeability or protein leakage.