Protein Electrophoresis (Pleural Fluid)

Protein in pleural fluid helps classify an effusion as transudate or exudate. Elevated pleural protein (often assessed with the pleural/serum protein ratio and Light’s criteria) suggests exudative causes such as infection, malignancy, pulmonary embolism, or inflammatory disease due to increased capillary permeability or lymphatic obstruction. Low protein favors transudative causes like heart failure, cirrhosis, or nephrotic syndrome.

Protein electrophoresis separates serum proteins into albumin and globulin fractions to reveal abnormal patterns. It detects monoclonal spikes (suggesting multiple myeloma or other plasma-cell disorders), polyclonal increases (inflammation or chronic infection), low immunoglobulins (immunodeficiency), and changes seen with liver disease or nephrotic syndrome. It helps diagnose conditions and monitor disease progression and treatment response.

Pleural fluid in tuberculous effusion is typically exudative, with total protein usually >3.0 g/dL (commonly 3–5 g/dL) and a pleural fluid/serum protein ratio >0.5. These values reflect increased capillary permeability and help distinguish TB effusions from transudates. Clinical interpretation should use Light’s criteria alongside cell counts and ADA for accurate diagnosis.

Yes—nucleic acid amplification tests (PCR/NAAT, e.g., Xpert) can be performed on pleural fluid to detect Mycobacterium tuberculosis and rifampicin resistance. Sensitivity is lower than sputum or pleural biopsy/culture, so a negative PCR does not exclude tuberculous pleural effusion. Diagnostic yield improves by combining PCR with pleural fluid ADA, microscopy/culture, and thoracoscopic or image-guided pleural biopsy.

Malignant pleural effusion is suggested by unilateral, recurrent, often blood‑tinged effusions; fluid analyses show an exudate with high LDH, low glucose and low pH. Definitive diagnosis requires identification of malignant cells on pleural fluid cytology or tissue obtained by image‑guided biopsy or thoracoscopy. If cytology is negative but clinical suspicion persists, pleural biopsy and imaging (CT/PET) help confirm malignancy.

Pleural fluid can help detect tuberculous pleuritis, but direct detection is often limited: acid‑fast smears are insensitive, cultures improve yield but take weeks, and nucleic acid amplification tests increase sensitivity. High pleural fluid adenosine deaminase or interferon‑gamma strongly suggests TB. Pleural biopsy for histology and culture gives the highest diagnostic yield; combined tests and clinical context guide diagnosis.