Light's criteria define an exudative pleural effusion by which finding?

Light's criteria define an exudative pleural effusion by which finding?

• A. Pleural fluid protein ratio >0.5 and LDH ratio >0.6
• B. Pleural fluid protein ratio >0.7 and LDH ratio >0.6
• C. Pleural fluid protein ratio >0.3 and LDH ratio >0.9
• D. Pleural fluid protein ratio >0.4 and LDH ratio >0.4

Answer: (A)

Light's criteria help distinguish an exudative pleural effusion from a transudate by comparing pleural fluid components to serum. An exudate is present if any of these are true: the pleural fluid protein to serum protein ratio is greater than 0.5; the pleural fluid LDH to serum LDH ratio is greater than 0.6; or the pleural fluid LDH is greater than two-thirds the upper limit of normal serum LDH. These patterns reflect inflammation or malignancy causing increased vascular permeability and protein/LDH leakage into the pleural space. In this item, the option that aligns with the classic thresholds for protein and LDH ratios—protein ratio greater than 0.5 and LDH ratio greater than 0.6—best fits Light's criteria as commonly tested. The other options use thresholds that do not correspond to these standard cutoffs.

Light's criteria help distinguish an exudative pleural effusion from a transudate by comparing pleural fluid components to serum. An exudate is present if any of these are true: the pleural fluid protein to serum protein ratio is greater than 0.5; the pleural fluid LDH to serum LDH ratio is greater than 0.6; or the pleural fluid LDH is greater than two-thirds the upper limit of normal serum LDH. These patterns reflect inflammation or malignancy causing increased vascular permeability and protein/LDH leakage into the pleural space.

In this item, the option that aligns with the classic thresholds for protein and LDH ratios—protein ratio greater than 0.5 and LDH ratio greater than 0.6—best fits Light's criteria as commonly tested. The other options use thresholds that do not correspond to these standard cutoffs.