Which of the following is NOT part of Light's criteria for exudative effusion?

Which of the following is NOT part of Light's criteria for exudative effusion?

• A. Pleural fluid protein/serum protein ratio > 0.5
• B. Pleural fluid LDH/serum LDH ratio > 0.6
• C. Pleural fluid LDH > 2/3 ULN
• D. Pleural fluid protein/serum protein ratio <= 0.5

Answer: (D)

Light's criteria distinguish exudative from transudative pleural effusions by three findings: a pleural fluid to serum protein ratio greater than 0.5, a pleural fluid to serum LDH ratio greater than 0.6, or a pleural fluid LDH higher than two-thirds the upper limit of normal for serum LDH. The statement with a pleural fluid protein to serum protein ratio of 0.5 or less does not fit these exudate criteria; it actually points to a transudate, where the pleural fluid protein is relatively low due to imbalances like hydrostatic or oncotic pressure, not inflammation or malignancy. Therefore, this option is not part of Light's criteria for exudative effusion.

Light's criteria distinguish exudative from transudative pleural effusions by three findings: a pleural fluid to serum protein ratio greater than 0.5, a pleural fluid to serum LDH ratio greater than 0.6, or a pleural fluid LDH higher than two-thirds the upper limit of normal for serum LDH. The statement with a pleural fluid protein to serum protein ratio of 0.5 or less does not fit these exudate criteria; it actually points to a transudate, where the pleural fluid protein is relatively low due to imbalances like hydrostatic or oncotic pressure, not inflammation or malignancy. Therefore, this option is not part of Light's criteria for exudative effusion.