Apply Light’s criteria to pleural and serum protein and LDH values to classify an effusion as exudate or transudate.
Result
How to use this tool
Use pleural fluid and serum protein in the same units.
Use pleural fluid and serum LDH in the same units, plus the local serum upper limit.
Each of the three tests is shown as met or not met.
Any one met criterion makes it an exudate; none met makes it a transudate.
Formula & worked example
Pleural protein 4 with serum protein 6 gives a ratio of 0.67 (above 0.5), pleural LDH 300 with serum LDH 200 gives 1.50 (above 0.6), and 300 exceeds two-thirds of an upper limit of 250 (167), so all 3 criteria are met: exudate.
Limitations — read this before you rely on it
Classification aid only. Diuretics, timing and concurrent disease can misclassify effusions, and the underlying cause still needs clinical work-up. This tool is for education only and is not medical advice. Talk to a clinician about any result that worries you, and never change treatment because of a calculator result.
Frequently asked questions
Three pleural-versus-serum comparisons that separate exudative from transudative effusions; any one met means exudate.
Usually raised hydrostatic or low oncotic pressure, classically heart failure, cirrhosis or nephrotic syndrome.
Usually pleural inflammation or impaired drainage, such as infection, malignancy or pulmonary embolism.
Yes. Diuretic treatment can raise protein and LDH ratios enough to misclassify a cardiac effusion.
Only that each pair uses the same units, since the criteria are ratios except for the upper-limit comparison.