Light's criteria are applied to a pleural fluid. Pleural fluid protein/serum protein ratio is 0.62, pleural LDH/serum LDH ratio is 0.72, and pleural LDH is 310 U/L (upper limit of serum LDH normal is 200 U/L). How should this effusion be classified?

• A Transudate — meets no Light's criteria
• B Exudate — meets two of three Light's criteria
• C Exudate — meets all three Light's criteria ✓
• D Transudate — pleural protein is the only relevant criterion

Explanation

Light's criteria classify a pleural fluid as an exudate if ANY ONE criterion is met: (1) pleural fluid protein/serum protein >0.5 — here 0.62 (YES), (2) pleural fluid LDH/serum LDH >0.6 — here 0.72 (YES), (3) pleural fluid LDH >2/3 upper limit of normal serum LDH — here 310 vs 200×(2/3)=133 U/L, so 310>133 (YES). All three criteria are positive, classifying this definitively as an exudate.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.