What LDH Stands For
LDH stands for lactate dehydrogenase (also called lactic acid dehydrogenase), which is an enzyme measured in blood and body fluids to assess tissue damage, cell death, and help distinguish between different types of pleural effusions. 1, 2
Clinical Context in Pleural Effusion Analysis
In the context of pleural fluid analysis, LDH serves as a critical biochemical marker with the following roles:
Primary Diagnostic Function
- LDH is a key component of Light's criteria, the gold standard for distinguishing exudative from transudative pleural effusions. 1, 3
- A pleural effusion is classified as an exudate when the pleural fluid LDH divided by serum LDH ratio is >0.6, OR when pleural fluid LDH is >2/3 (>67%) of the upper limit of normal for serum LDH. 1, 3
- Light's criteria using LDH demonstrate 98% sensitivity and 72% specificity for identifying exudates. 3
Prognostic Significance
- Elevated pleural fluid LDH levels (>1500 IU/L) correlate with worse survival in malignant pleural effusions across multiple cancer types. 1
- The LENT prognostic score for malignant pleural effusion incorporates pleural fluid LDH, with levels >1500 IU/L scoring 1 point and predicting shorter survival. 1
Practical Measurement Considerations
- LDH is measured as total enzymatic activity in both serum and pleural fluid samples, with the enzyme catalyzing the reversible conversion between lactate and pyruvate. 2
- The upper limit of normal for LDH is laboratory-specific and depends on the assay methodology used. 2
- In-vitro hemolysis of blood samples can falsely elevate LDH levels, so hemolyzed samples should be repeated. 4
Common Pitfall
- When pleural fluid protein is borderline (near 30 g/L), measuring both serum and pleural fluid LDH allows application of Light's criteria for more accurate classification than protein alone. 1