From the Guidelines
Laboratory evaluation of pleural effusion should begin with thoracentesis to collect fluid for analysis, including appearance assessment, cell count with differential, protein, LDH, glucose, pH, and microbiological studies, to classify the effusion as a transudate or exudate using Light's criteria, as outlined in the most recent European Respiratory Journal study 1. The initial tests should include:
- Appearance assessment (clear, cloudy, bloody)
- Cell count with differential
- Protein
- LDH
- Glucose
- pH
- Microbiological studies (Gram stain and culture) These basic tests help classify the effusion as either a transudate or exudate using Light's criteria: exudates have pleural fluid/serum protein ratio >0.5, pleural fluid/serum LDH ratio >0.6, or pleural fluid LDH >2/3 the upper limit of normal serum LDH, as stated in the European Respiratory Journal study 1. Additional specialized tests may be ordered based on clinical suspicion, including:
- Cytology for malignancy
- Amylase for pancreatic disease or esophageal rupture
- Triglycerides for chylothorax (>110 mg/dL suggests chylous effusion)
- Adenosine deaminase for tuberculosis
- NT-proBNP for heart failure These laboratory tests are crucial for determining the underlying cause of pleural effusion, which guides appropriate treatment, as discussed in the American Journal of Respiratory and Critical Care Medicine study 1. For example, infectious effusions require antibiotics, malignant effusions may need oncologic intervention, and transudative effusions from heart failure require diuretics and cardiac management, as outlined in the Intensive Care Medicine study 1.
From the Research
Pleural Effusion Lab
- Pleural effusion is an excessive accumulation of fluid in the pleural space, which can be related to disorders of the lung or pleura, or to a systemic disorder 2.
- The diagnostic evaluation of pleural effusion includes chemical and microbiological studies, as well as cytological analysis, which can provide further information about the etiology of the disease process 2.
- Laboratory testing helps to distinguish pleural fluid transudate from an exudate, and immunohistochemistry provides increased diagnostic accuracy 2, 3.
- The most common causes of pleural effusion are congestive heart failure, cancer, pneumonia, and pulmonary embolism 4, 5.
- Pleural fluid puncture (pleural tap) enables the differentiation of a transudate from an exudate, which remains the foundation of the further diagnostic work-up 5.
- Specific biomarkers, such as natriuretic peptides for heart failure, adenosine deaminase for tuberculosis, or mesothelin for mesothelioma, can be used to aid in the diagnosis of pleural effusions 3.
Diagnostic Approach
- A combination of medical history, physical examination, imaging tests, and pertinent pleural fluid analyses is used to determine the etiology of pleural effusions 3.
- Invasive procedures, such as pleuroscopic biopsies, may be required for persistently symptomatic effusions which remain undiagnosed after the analysis of one or more pleural fluid samples 3.
- Image-guided biopsies should be attempted first when parietal pleural nodularity or thickening exist 3.
- A practical approach to the diagnosis and management of pleural effusions includes identifying the most common causes and using a step-by-step approach to determine the underlying cause 4, 6.
Management
- The treatment of pleural effusion depends on the underlying cause, and may include treating the underlying medical disorder, draining the effusion, or performing pleurodesis 2, 5.
- Malignant effusions are usually drained to palliate symptoms and may require pleurodesis to prevent recurrence 2.
- Empyemas need to be treated with appropriate antibiotics and intercostal drainage, and surgery may be needed in selected cases 2.