Light's Criteria Calculator
Determine if pleural effusion is exudate or transudate using protein and LDH ratios
Critical Medical Disclaimer
This calculator is for educational purposes only and should NOT be used for medical diagnosis or treatment decisions.
- Light's criteria interpretation requires comprehensive clinical assessment
- Laboratory values must be obtained simultaneously from pleural fluid and serum
- Additional clinical factors, imaging, and symptoms are essential for diagnosis
- Always consult a pulmonologist or physician for proper pleural effusion evaluation
Light's Criteria Assessment
Protein concentration in pleural fluid sample
Protein concentration in blood serum (same time as pleural sample)
Lactate dehydrogenase in pleural fluid
Lactate dehydrogenase in blood serum
Laboratory-specific upper normal limit for LDH (varies between labs, typically 200-250 U/L)
Light's Criteria Results
Interpretation: Enter laboratory values for classification
Formula: Protein ratio = Pleural protein ÷ Serum protein; LDH ratio = Pleural LDH ÷ Serum LDH
Clinical Significance
Example Calculations
Exudate Example (Pneumonia)
Pleural protein: 4.2 g/dL, Serum protein: 6.8 g/dL
Pleural LDH: 350 U/L, Serum LDH: 200 U/L, Upper normal: 250 U/L
Protein ratio: 4.2÷6.8 = 0.62 (≥0.5 ✓)
LDH ratio: 350÷200 = 1.75 (≥0.6 ✓)
LDH/Upper limit: 350÷250 = 1.40 (≥0.67 ✓)
Result: Exudate (3/3 criteria met)
Transudate Example (Heart Failure)
Pleural protein: 1.8 g/dL, Serum protein: 6.2 g/dL
Pleural LDH: 110 U/L, Serum LDH: 190 U/L, Upper normal: 250 U/L
Protein ratio: 1.8÷6.2 = 0.29 (<0.5 ✗)
LDH ratio: 110÷190 = 0.58 (<0.6 ✗)
LDH/Upper limit: 110÷250 = 0.44 (<0.67 ✗)
Result: Transudate (0/3 criteria met)
Light's Criteria
Exudate Criteria (≥1 required)
Additional Parameters
Common Causes
Exudate
Transudate
Clinical Notes
Blood and pleural fluid samples must be drawn simultaneously
Upper normal LDH limit varies by laboratory (typically 200-250 U/L)
Light's criteria has 98% sensitivity for exudates
Consider clinical context - some heart failure cases may meet exudate criteria
Understanding Light's Criteria
What are Light's Criteria?
Light's criteria are laboratory-based rules used to distinguish between exudative and transudative pleural effusions. Developed by Dr. Richard Light in 1972, these criteria help determine the underlying cause of fluid accumulation in the pleural space.
Clinical Importance
- •Guides diagnostic workup and treatment approach
- •98% sensitivity for detecting exudates
- •Helps prioritize further investigations
- •Assists in determining need for pleural biopsy
Pathophysiology
Important: Light's criteria should be interpreted with clinical context. Some conditions like heart failure on diuretics may occasionally meet exudate criteria.
Diagnostic Algorithm
Step 1: Obtain Samples
Collect simultaneous pleural fluid and serum samples for protein and LDH analysis.
Step 2: Apply Criteria
Calculate ratios and determine if any of the three Light's criteria are met for exudate classification.
Step 3: Clinical Correlation
Integrate results with clinical presentation, imaging, and additional tests as needed.