Evaluation of Pleural Fluid Studies

Last updated: April 6, 2026, 10:53 PM Pacific Time (PDT)

Interactive teaching tool for Light's criteria, exudative versus transudative pleural effusion patterns, and likely causes from pleural fluid studies.

All Light's criteria Exudate Transudate Add-on tests Back to Main Page

Interactive pleural fluid calculator

Pleural fluid labs to order
Core labs
Optional labs
Light's criteria
Complication clues
Clinical context

Calculated interpretation

Likely diagnoses or causes

Recommended next labs, imaging, and diagnostics

Flowchart

First pass
Classify by Light's criteria
If any Light's criterion is met, classify as exudative. If none are met, transudative is more likely.
Light's criteria
  • Pleural protein / serum protein > 0.5
  • Pleural LDH / serum LDH > 0.6
  • Pleural LDH > 2/3 serum LDH upper limit of normal
Transudate
  • Heart failure
  • Cirrhosis / hepatic hydrothorax
  • Nephrotic syndrome or hypoalbuminemia
Exudate
  • Parapneumonic effusion or empyema
  • Malignancy
  • PE
  • TB or inflammatory pleuritis
Add-on tests
  • pH/glucose/Gram stain/culture for infection
  • Cytology for malignancy
  • Triglycerides for chylothorax
  • ADA/AFB when TB is plausible