Pleural fluid accumulates between the lung and chest wall due to various diseases.

Analysis helps differentiate between transudative and exudative effusions using Light’s criteria.

Clinical uses include:

Diagnosing infections (e.g., tuberculosis, pneumonia, empyema).

Detecting malignancy (lung cancer, metastatic disease).

Evaluating systemic conditions (heart failure, liver cirrhosis, nephrotic syndrome).

Assessing autoimmune or inflammatory disorders.

Often performed alongside cytology, culture, and biochemical tests for a complete evaluation.

Analytes commonly measured:

Appearance: Clear, turbid, bloody, or purulent.

Protein & LDH: Used in Light’s criteria to classify effusion.

Glucose: Low in infections, rheumatoid effusion, or malignancy.

pH: Low in empyema or complicated effusions.

Cell count & differential: Neutrophils (infection), lymphocytes (TB, malignancy).

Cytology: Detects malignant cells.

Microbiology: Gram stain, culture, AFB stain for TB.

Normal Result: No abnormal accumulation of fluid.

Abnormal Findings:

Transudate: Low protein, low LDH (seen in CHF, cirrhosis, nephrotic syndrome).

Exudate: High protein, high LDH (seen in infection, malignancy, inflammation).

Clinical Use:

Provides a comprehensive diagnostic tool for pleural effusion.

Helps guide management in pulmonology, oncology, and infectious disease.