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Pleural fluid: cytology
Overview
- Pleural fluid occurs within the thoracic cavity. Very little or no fluid can be aspirated unless effusion is present.
- Normal fluid is clear and colorless to slightly yellow and is of low cellularity (<1000 nucleated cells/ml) and low protein >/-2.5 g/dl).
- Four mechanisms result in cavity effusions:
- Transudate - low specific gravity fluid crosses membrane barrier.
- Exudate - inflammation allows fluid with high cellular and protein component to cross vessel walls.
- Vessel or viscous rupture.
- Neoplastic proliferation.
- Cell characteristics vary in septic conditions and with neoplasia.
- Cytology enables finer differentiation of type of abdominal effusion Peritoneal fluid: differential cell count.
Uses
Alone
- Classification or diagnosis of cause of pleural effusion Pleural: effusion.
- Differentiate malignant from non-malignant effusions.
- Differentiate septic from non-septic effusions.
- Diagnosis of lymphoma Lymphoma or mast cell tumor Skin: mastocytoma when neoplastic cells are exfoliated into the effusion.
- Diagnosis of other forms of neoplasia, eg carcinoma Adenoma / adenocarcinoma , mesothelioma Mesothelioma.
Reactive mesothelial cells may resemble neoplastic mesothelial cells or carcinoma cells.
In combination
- With body fluid analysis including cell count Pleural fluid: differential cell count and refractometer protein Pleural fluid: protein to identify type of pleural effusion.
Other points
Many intrathoracic tumors may result in pleural effusion due to inflammation, eg if tumor is necrotic, or increased hydrostatic pressure but tumor cells are not necessarily exfoliated into the effusion.
Sampling
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Tests
Methodologies
- Direct smear of drop as for blood smear.
- Cytocentrifuge preparations or other special methods for concentration may be available at some commercial laboratories.
- For fluids of low cellularity:
- Centrifuge at 100 rpm for 10 min.
- Pour off supernatant.
- Flick tube to resuspend sediment.
- Put 1 drop onto slide.
- Make smear as for blood smear or use pull-apart/squash method using 2 slides.
- Romanowsky-type stains most commonly used for cytologic evaluation.
Availability
- Widely available at commercial laboratories.
- Smears can be examined in practice.
Validity
Sensitivity
- As with any cytologic specimen absence of evidence does not provide conclusive support for absence of a particular condition.
Specificity
- As with any cytologic specimen absence of evidence does not provide conclusive support for absence of a particular condition.
Technique intrinsic limitations
- Cytologic evaluation may be compromised by excessive blood contamination.
Technician extrinsic limitations
- May be difficult to differentiate reactive mesothelial cells from some neoplastic cells, eg carcinoma/adenocarcinoma/mesothelioma.
Result Data
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Further Reading
Publications
Refereed papers
- Recent references from VetMedResource and PubMed.
- McCullough S et al (1999) Collection and interpretation of respiratory cytology. Clin Tech Small Anim Pract 14, (4) 220-6.
- Dunn J K & Villiers E (1998) Cytological and biochemical assessment of pleural and peritoneal effusions. In Practice 20, 501-505.
- Steyn P F & Wittum T E (1993) Radiographic epiemiologic and clinical aspects of simultaneous pleural and peritoneal effusions in dogs and cats - 48 cases (1982-1991). JAAHA 202, 307-312.
- Wadle J R & Giger U (1990) Lipoprotein electrophoresis differentiation of chylous and nonchylous pleural effusions in dogs and cats and its correlation with pleural effusion triglycerole concentration. Comp Cont Ed Pract Vet 10, 121-136.
- Meyer D J & Franks P T (1987) Effusion - classification and cytologic examination. Comp Cont Ed Pract Vet 9, 123-128.
Other sources of information
- Cowell R L, Tyler R D & Meinkoth J H (1999) Diagnostic Cytology and Hematology of the Dog and Cat. 2nd edn. Mosby, USA.
- Duncan J R, Prasse K W & Mahaffey E A (1994) Veterinary Laboratory Medicine. Clinical Pathology. 3rd edn. Iowa University Press, USA.