Light's Criteria Calculator - Pleural Effusion Classification

Your details

Total protein concentration in the pleural fluid sample (thoracentesis specimen).
g/dL
Total protein concentration in a simultaneously drawn serum sample.
g/dL
Lactate dehydrogenase activity in the pleural fluid sample.
U/L
Lactate dehydrogenase activity in a simultaneously drawn serum sample.
U/L
The upper limit of the normal reference range for serum LDH at your laboratory. This value varies by lab; 240 U/L is a common reference.
U/L
ClassificationExudate
Exudate

Exudate or Transudate based on Light's criteria

Criteria met3
Protein ratio (fluid/serum)0.643
LDH ratio (fluid/serum)1.273
Pleural LDH / upper-normal LDH1.167
Protein ratio (threshold 0.5)0.643
LDH ratio (threshold 0.6)1.273
Pleural LDH fraction (threshold 0.667)1.167

Exudative effusion: 3 of 3 Light criteria positive.

  • 3 of the 3 Light criterionia are positive: only 1 is needed to classify as an exudate.
  • Protein ratio is 0.643 (threshold >= 0.5): suggests protein-rich fluid from inflammation or cell damage.
  • LDH ratio is 1.273 (threshold >= 0.6): elevated pleural LDH reflects local cellular injury or inflammation.
  • Pleural LDH is 116.7% of the upper normal serum LDH limit (threshold >= 66.7%): indicates active pleural inflammation.
  • Common causes of exudative effusions include pneumonia (parapneumonic), malignancy, tuberculosis, pulmonary embolism, and autoimmune diseases.

Next stepFurther workup of an exudative effusion typically includes pleural fluid cytology, culture, pH, glucose, and cell differential to narrow the cause. Consider chest CT and specialist referral.

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