In a patient with large pleural effusion, Light's criteria are used to distinguish exudate from transudate. Which set correctly defines an EXUDATE?
- A Pleural protein/serum protein < 0.5 AND pleural LDH < 200 IU/L
- B Pleural protein/serum protein > 0.5, OR pleural LDH/serum LDH > 0.6, OR pleural LDH > 2/3 upper normal serum LDH ✓
- C Pleural protein > 3 g/dL alone is sufficient
- D Specific gravity > 1.020 alone confirms exudate
Correct answer: B. Pleural protein/serum protein > 0.5, OR pleural LDH/serum LDH > 0.6, OR pleural LDH > 2/3 upper normal serum LDH
Explanation
Light's criteria (1972) define a pleural exudate if ANY ONE of the following is met: (1) pleural fluid protein / serum protein ratio > 0.5; (2) pleural fluid LDH / serum LDH ratio > 0.6; (3) pleural fluid LDH > 2/3 the upper limit of normal for serum LDH. If none of these criteria is met, the effusion is a transudate. Light's criteria have ~98% sensitivity but ~83% specificity for exudates; the serum-effusion albumin gradient (>1.2 g/dL suggests transudate) improves specificity in borderline cases.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.