Table 1. Biochemistry of pleural effusion markers used to diagnose pleural disease.

Biomarker	Differential disease
Glucose	Low glucose (<3.4 mmol/L); Complicated parapneumonic effusion, empyema, rheumatoid pleuritis, pulmonary tuberculosis, malignancy, esophageal rupture
Amylase	Pancreatic disease, esophageal rupture, pleural malignancy
pH	Pleural acidosis (pH <7.30); malignant effusion, complicated pleural infection, connective tissue disease, tuberculous pleural effusion, esophageal rupture
Pleural fluid differential cell counts	Predominant lymphocytosis; malignancy, tuberculosis, cardiac failure. Neutrophil dominant;parapneumonic effusion, pulmonary embolism, acute tuberculosis, benign asbestos pleural effusion
ADA	ADA >40 U/L; tuberculosis pleurisy

Based on the biomarker of pleural fluid, differential diagnosis is decided. This table is modified from BTS pleural disease guideline (1). ADA, adenosine deaminase.