Felis ISSN 2398-2950

Pleural fluid: cytology

Contributor(s): Kathleen P Freeman, Karen L Gerber, Andy Torrance

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 ot cross vessel walls.
    • Vessel or viscous rupture.
    • Neoplastic proliferation.
  • Examination of cell morphology helps to distinguish sterile and septic exudates.
  • Sometimes neoplastic cells are recognized (especially in lymphoma Lymphoma)   →   a non-invasive technique for diagnosing intrathoracic neoplasia.
  • Cytology enables finer differentiation of type of pleural effusion.
  • Use in combination with cell count and differential Pleural fluid: differential cell count, protein Pleural fluid: protein, culture Pleural fluid: culture and sensitivity.

Sampling

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Tests

Methodologies

  • Direct smear from drop of fluid using blood smear technique.
  • Cetrifuge Centrifuge sample and make smear from sediment.
  • For fluids of low cellularity:
    • Centrifuge at 100 rpm for 10 min.
    • Pour off supernanatant (care should be taken to observe specimen during pour-off since viscous pleural fluid may result in loss of sediment).
    • Flick tube to suspend sediment.
    • Put 1 drop on 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.
  • Cytocentrifuge preparations or other special methods for concentration may be available at some commercial laboratories.

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.

Technician (extrinsic) limitations

  • May be difficult to differentiate reactive mesothelial cells from some neoplastic cells.
    Send for expert analysis.

Result Data

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Further Reading

Publications

Refereed papers

  • Recent references from VetMed Resource 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 & Villers E (1998) Cytological and biochemical assessment of pleural and peritoneal effusions. In Practice 20, 501-505.
  • Rishniw M et al(1998) Hydrothorax secondary to a perinephric pseudocyst in a cat. Vet Radiol Ultrasound 39(3), 193-196.
  • Fossum T W et al(1992) Severe bilateral fibrosing pleuritis associated with chronic chylothorax in five cats and two dogs. JAVMA 201(2), 317-324.
  • Hawkins E C et al(1986) Immunoglobulin A myeloma in a cat with pleural effusion and serum hyperviscosity. JAVMA 188(8), 876-878.

Other sources of information

  • Baker R & Lumsden J H (2000) Pleural and Peritoneal Fluids. In: Color Atlas of Cytology of the Dog and Cat. Mosby, St Louis. pp 159-165. ISBN 0 8151 0402 2.
  • Cowell R L, Tyler R D & Meinkoth J H (1999) Diagnostic Cytology and Hematology of the Dog and Cat. 2nd edn. Mosby, St. Louis.
  • Duncan J R, Prasse K W & Mahaffey E A (1994) Veterinary Laboratory Medicine. In: Clinical Pathology. 3rd edn. Iowa State University Press.
  • Cowell R L, Tyler R D & Meinkoth J H (1989) Abdominal and thoracic fluid. In: Diagnostic Cytology of the Dog and Cat.1st edn. American Veterinary Publications Ltd. pp 151-166.


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