Peritoneal fluid examination

Keywords: Ascitic fluid


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.


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.


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


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.


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.

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