Pleural/pericardial fluid exam

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 be submitted for cytology; add heparin (at a final concentration of 5 U/mL of fluid) or sodium citrate as an anticoagulant. 

A biopsy may be collected at the time of aspiration, and unfixed fluid sent for cell surface markers if lymphoma is suspected.

Refrigerate if more than 24 h delay to laboratory.

Clinical information is essential.

Macroscopic examination. 

Additional tests as appropriate: 

microscopic examination - wet film, Gram stain, special stain for AFB;

bacterial culture including Mycobacterium tuberculosis; Protein, Glucose, Amylase, Lactate dehydrogenase, Lactate dehydrogenase isoenzymes; and

centrifugation followed with Papanicolaou and Romanowsky stained smears for cytology plus cytocentrifugation/cell blocks for immunohistochemistry (differential diagnosis particularly between carcinoma, mesothelioma, and marked reactive mesothelial atypia).

Investigation of effusions;

inflammatory conditions (including possible bacterial, viral and fungal infections); and

suspected primary or secondary neoplasm.

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. 

Lactate dehydrogenase 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, including lymphoma. 

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, as well as reactive/inflammatory changes.