From the Guidelines
High LDH in pleural fluid is a strong indicator of an exudative pleural effusion, which requires further diagnostic testing and treatment of the underlying condition, as stated in the British Thoracic Society guideline for pleural disease 1. When pleural fluid LDH is high, it suggests an exudative effusion, which is typically caused by conditions that increase capillary permeability or impair lymphatic drainage, such as infections, malignancies, pulmonary embolism, rheumatologic diseases, or pancreatitis.
- The elevated LDH occurs because of increased cellular breakdown and inflammation in these conditions.
- According to the guideline, pleural fluid is considered an exudate if one or more of the following criteria are met: + Pleural fluid protein divided by serum protein is > 0.5 + Pleural fluid lactate dehydrogenase (LDH) divided by serum LDH is > 0.6 + Pleural fluid LDH > 2/3 the upper limits of laboratory normal value for serum LDH
- Further diagnostic testing is usually needed, including cytology, cultures, glucose levels, pH, and specific biomarkers depending on the suspected underlying cause, as suggested by the BTS guidelines for the management of pleural infection 2, 3.
- Treatment focuses on addressing the primary condition rather than the LDH level itself, and the LDH level can also be useful for monitoring treatment response in certain conditions, with decreasing levels often indicating improvement in the underlying inflammatory or infectious process.
- It is essential to note that the presence of high LDH in pleural fluid, along with other biochemical criteria such as low pH and low glucose levels, can indicate the need for chest tube drainage, as stated in the BTS guidelines 3.
From the Research
Pleural Fluid High LDH
- High LDH levels in pleural fluid can indicate an exudative pleural effusion, which is often caused by infections, malignancies, or inflammation 4, 5, 6.
- According to Light's criteria, an LDH level greater than two-thirds the upper limit of normal for serum LDH can help differentiate between transudative and exudative pleural effusions 4, 6.
- A study found that an LDH level greater than 200 U/L in pleural fluid had a likelihood ratio of 18 for diagnosing an exudate 6.
- Another study suggested that an LDH/ADA ratio in pleural fluid can be useful in distinguishing between parapneumonic and non-parapneumonic pleural effusions, with a sensitivity and specificity of 98.06% and 98.08%, respectively 7.
- High LDH levels in pleural fluid can also be associated with a poor prognosis, particularly if the level is greater than three times the upper limit of normal in serum 4.
Diagnostic Approach
- The diagnosis of pleural effusion should involve a combination of clinical presentation, chest imaging findings, and pleural fluid analysis 5.
- Pleural fluid analysis should include measurements of protein, LDH, and adenosine deaminase (ADA) levels, as well as cytological examination and culture 4, 5, 8.
- Thoracocentesis and pleural biopsy can also be useful in diagnosing pleural diseases, particularly in cases where pleural fluid analysis is inconclusive 8.
Clinical Implications
- High LDH levels in pleural fluid can guide treatment decisions, such as the use of antibiotics or anti-inflammatory medications 4, 5.
- In cases of malignant pleural effusions, high LDH levels can indicate a poor prognosis and may influence the decision to perform pleurodesis or other palliative procedures 4.