Analyte

Abnormal result

Cause

Glucose

<3.4 mmol/L (60 mg/dL)

Malignant or parapneumonic effusion, pleural empyema, tuberculosis

<1.6 mmol/L (29 mg/dL)

Pleural empyema, rheumatoid arthritis

pH

<7.2

Parapneumonic effusion with complications, pleural empyema, esophageal perforation

Triglycerides

>1.24 mmol/L (110 mg/dL)

Chylothorax (if chylomicrons and no cholesterol crystals are observed)

Cholesterol

>5.18 mmol/L (200 mg/dL) and crystals

Pseudochylothorax

Amylase

Increased activity

Acute pancreatitis, esophageal rupture, pleural malignancies (particularly adenocarcinoma)

ADA

≥40 IU/L

Tuberculous pleuritis (identification of the ADA-2 isoform increases test specificity)

Hematocrit

≥50% of peripheral blood hematocrit

Hemothorax

Neutrophils

Present

Bacterial infection, pulmonary embolism

Lymphocytes

Present

Tuberculosis, malignancies

Eosinophils

>10%

Asbestosis, malignancy, parasitic infestation, granulomatosis with polyangiitis, drug-induced reaction, hemothorax or pneumothorax

Light criteria for differentiation between transudates and exudates: proteinfluid/proteinserum >0.5, LDHfluid/LDHserum >0.6, LDHfluid/LDHserum ULN >2/3; each of these criteria indicates an exudate.