skip to main content

Light's Criteria Effusion — FRCA Final MCQ

Instant feedback + full explanation. One question, done properly.

ModerateIntensive Care MedicineLight's Criteria EffusionFRCA Final

A 55-year-old man (ASA III) in ICU has a right-sided pleural effusion drained by an intercostal chest drain. Three litres of straw-coloured fluid are obtained. Light's criteria are applied: pleural fluid protein 42 g/L (serum 62 g/L), pleural fluid LDH 250 U/L (serum 300 U/L). The fluid protein/serum protein ratio is 0.68. What type of effusion is this?

Educational content. Not a substitute for clinical judgement or local policy.

Reveal the answer and explanation

Correct answer: E — Exudate

Light's criteria classify an effusion as an EXUDATE if ANY ONE of: (1) pleural fluid protein/serum protein ratio >0.5, (2) pleural fluid LDH/serum LDH ratio >0.6, (3) pleural fluid LDH >2/3 upper limit of normal serum LDH. This patient's protein ratio = 42/62 = 0.68 (>0.5) – EXUDATE. Exudative effusions suggest pathology: infection, malignancy, PE, autoimmune disease, or pancreatitis. Transudates (heart failure, cirrhosis, nephrotic syndrome) fail all three criteria.

Reference: BTS – 2023 – Pleural disease guidelines; Light RW – 1972 – Light's criteria