Peritoneal fluid examination

Keywords: Ascitic fluid

Specimen:

Ascitic, peritoneal fluid in separate, sterile containers for microbiology, chemical pathology and cytology.

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.

Refrigerate if more than 24 h delay to laboratory.

Clinical information is essential.

Peritoneal washings should be treated in the same manner as above.

Method:

Macroscopic examination. Additional tests as appropriate: microscopic examination (wet film, cell count, differential count, Gram stain, bacterial culture); measurement of glucose, protein, amylase, if appropriate; and cytology. 

Additional tests if appropriate: stains and culture (large volume) for Mycobacterium tuberculosis; and Lactate dehydrogenase, Lactate dehydrogenase isoenzymes.

Centrifugation followed with Papanicolaou and Romanowsky stained smears for cytology plus cytocentrifugation/cell blocks for immunohistochemistry.

Application:

Investigation of peritonitis, ascites, peritoneal fluid collections; staging/localised spread of gynaecological neoplasm.

Interpretation:

An increase in neutrophils (>250 x 106L) is considered diagnostic of peritonitis (bacterial, tuberculous, pancreatic or malignant). 

Protein levels >25 g/L (exudate) favour inflammatory or malignant ascites. 

Amylase activity is increased in Pancreatitis. 

Occasionally Lactate dehydrogenase isoenzymes may help to determine the cause of an exudate: 

LD5 is derived from neutrophils;

LD2 and LD3 suggest malignancy; and

LD1 and LD2 are derived from red cells.

A negative culture does not exclude the diagnosis of bacterial Peritonitis.

Cytology may detect primary or metastatic malignancy.

Interpretation of borderline/low grade lesions may prove difficult in peritoneal washings and are therefore reported in conjunction with accompanying histology.

Reference:

Mandell GL. Principles and Practice of Infectious Diseases. 7th ed. 2009. Churchill Livingstone.

Gray W and Kocjan G eds. Diagnostic Cytopathology.  3rd ed. 2010. Churchill Livingstone.