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PulmonologyLight et al. 1972 · Clinical Decision Tool

Light's Criteria

Pleural Effusion Classification — Transudate vs Exudate · Enter pleural fluid and serum values for instant interpretation with clinical guidance
Step 1 — Enter Laboratory Values

Pleural fluid and serum results

Enter pleural fluid and corresponding serum values. All three criteria are calculated simultaneously — live ratios update as you type.
Protein
g/dL
g/dL
LDH (Lactate Dehydrogenase)
U/L (IU/L)
U/L (IU/L) — normal upper limit typically 200–240 U/L
Lab-specific upper limit of normal (ULN) for serum LDH
U/L — varies by laboratory (typically 200–240 U/L)
Live criteria evaluation
Criterion 1 — Pleural : Serum Protein Ratio
Exudate if > 0.5
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Criterion 2 — Pleural : Serum LDH Ratio
Exudate if > 0.6
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Criterion 3 — Pleural fluid LDH vs ²⁄₃ ULN serum LDH
Exudate if > ²⁄₃ ULN (— U/L)
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Reference: Light RW, Macgregor MI, Luchsinger PC, Ball WC Jr. Pleural effusions: the diagnostic separation of transudates and exudates. Ann Intern Med. 1972;77(4):507-513. Light's criteria have a sensitivity of ~98% and specificity of ~83% for exudates. The two-test rule (albumin gradient and LDH) may identify misclassified cases. ProtoMD is an assistive tool — not a substitute for professional clinical judgment.