PLEURAL/PERICARDIAL FLUID EXAMINATION

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Specimen: Initially, fluid is collected into a plain sterile container for microbiology and chemical pathology. A large volume should be submitted if tuberculous infection is suspected. As much fluid as possible should also be submitted for cytology; heparin (at a final concentration of 5U/mL of fluid) should be added as an anticoagulant. A biopsy is usually collected at the time of aspiration, if malignancy is suspected.

Method: Macroscopic examination. Additional tests as appropriate: microscopic examination - wet film, Gram stain, special stain for AFB; bacterial culture incl Mycobacterium tuberculosis; protein, glucose, amylase, LD, LD isoenzymes; cytology.

Application: Investigation of effusions; inflammatory conditions, including possible bacterial, viral and fungal infections; possible malignancy.

Interpretation: Exudates are characterised by protein levels of >25 g/L; commonly associated with malignancy, pneumonia, tuberculosis. Transudates have protein levels of <25 g/L and are seen in congestive cardiac failure, cirrhosis, nephrotic syndrome, hypothyroidism, Meigs syndrome. LD isoenzymes in exudates may help identify the likely source: LD1 and LD2 - red cells; LD2 and LD3 - malignancy; LD5 - neutrophils. Neutrophils are increased in bacterial infection; lymphocytes may be increased in tuberculosis, malignancy. Glucose levels may be low in pleuritis or pericarditis due to rheumatoid arthritis. Amylase is raised in pleuritis associated with pancreatitis. Cytology may detect malignant cells from mesothelioma, metastatic or locally invasive tumours.

Reference: Vergnon JM et al. Cancer 1984; 54: 507-511. Koss LG. Diagnostic Cytology and its Histopathologic Basis. 4th ed. Lippincott 1992.

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