Healthcare & Clinical
Light's Criteria for Pleural Effusion (Exudate vs Transudate)
Classify thoracentesis pleural fluid as Exudate or Transudate using Light's 3-rule OR logic: Pleural/Serum Protein > 0.5, Pleural/Serum LDH > 0.6, or Pleural LDH > (2/3) * Serum LDH ULN.
Separate hydrostatic transudates from inflammatory or malignant exudates!
Under Richard Light's landmark diagnostic rule (~98% sensitivity for exudates), a pleural effusion is classified as an Exudate (pneumonia/parapneumonic, malignancy, pulmonary embolism, tuberculosis) if ANY ONE OR MORE of three biochemical thresholds is met: (1) Pleural Protein / Serum Protein > 0.50, (2) Pleural LDH / Serum LDH > 0.60, or (3) Pleural LDH > (2 / 3) * Upper Limit of Normal (ULN) for Serum LDH!
Only when ALL THREE criteria are simultaneously negative does the fluid classify as a Transudate (congestive heart failure, cirrhosis, nephrotic syndrome)! If a heart-failure patient on aggressive diuretics narrowly triggers an exudate by protein ratio alone, clinicians follow up with the Serum-to-Pleural Protein Gradient (> 3.1 g/dL favors pseudo-exudative CHF transudate).
| Light's Criterion | Exudate Cutoff | Parapneumonic Case | CHF Heart Failure Case |
|---|---|---|---|
| 1. Pleural / Serum Protein Ratio | > 0.50 | 3.8 / 6.8 = 0.559 (POSITIVE) | 2.1 / 6.8 = 0.309 (Negative) |
| 2. Pleural / Serum LDH Ratio | > 0.60 | 260 / 320 = 0.813 (POSITIVE) | 95 / 320 = 0.297 (Negative) |
| 3. Pleural LDH vs (2/3)*Serum ULN (240) | > 160 IU/L | 260 > 160 (POSITIVE -> Exudate) | 95 <= 160 (ALL 3 Neg -> Transudate) |
Light's 3-Rule OR Classification Formula
Tests all three ratios simultaneously with OR(...) after verifying positive serum denominators B3, B5, and B6.
=IF(OR(B3 <= 0, B5 <= 0, B6 <= 0), "Invalid Serum Lab Reference", IF(OR((B2 / B3) > 0.5, (B4 / B5) > 0.6, B4 > ((2 / 3) * B6)), "Exudative Effusion", "Transudative Effusion"))Count Positive Light's Criteria (0 to 3 Score)
Converts each boolean condition to 0/1 with --(...) so pulmonologists see whether 0, 1, 2, or all 3 criteria triggered.
=--((B2 / B3) > 0.5) + --((B4 / B5) > 0.6) + --(B4 > ((2 / 3) * B6))Try the example
Use the original values or change them to test your understanding.