Felis ISSN 2398-2950

Bronchial-tracheal wash: cytology

Synonym(s): Bronchoalveolar lavage BAL, Tracheal aspiration, Tracheal wash TW

Contributor(s): Kathleen P Freeman, Karen L Gerber, Francesco Cian

Overview

  • Used to obtain cells and secretions to identify the cause of respiratory tract disease by cytology and microbiology.
  • Sample may be obtained in a conscious cat by a transtracheal wash (percutaneously) Transtracheal wash, or under anesthesia through an endotracheal tube, or by endoscopy.
  • Used where there are clinical signs and evidence on diagnostic imaging of tracheal or bronchoalveolar disease to evaluate pathology, to assist in therapeutic choices.

Sampling

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Tests

Methodologies

  • Direct smears (helpful if made at time of collection) and centrifuged preparations.
  • Cytospin or centrifuged preparations are made at 1000 rpm (slow speed) for 5 min.
  • Romanowsky stains commonly used for air-dried preparations.
  • Light microscopy.

Validity

Sensitivity

  • Variable depending on degree of inflammation, type of condition, and whether or not a representative specimen has been obtained.
  • BAL is more likely to obtain a representative specimen of lower airway disease than a tracheal wash.
  • Neoplasia will only be detected if the neoplastic cells have eroded the bronchiolar/alveolar surface, in order to exfoliate into the respiratory lumen.

Specificity

  • Variable depending on degree of inflammation, type of condition, and whether or not a representative specimen has been obtained.
  • Bacterial cultures should be interpreted with caution if the cytologist has identified evidence of oropharyngeal contamination.
  • The presence of columnar respiratory epithelial cells in a BAL indicates that a portion of the sample has been collected from the tracheal region and might not necessarily reflect the bronchiolar-alveolar region.
  • Phagocytosis of bacteria, cell fragments and erythrocytes can occur in transit, this may increase the risk of cytological misinterpretation.
  • Marked dysplasia secondary to irritation or inflammation may mimic neoplasia.

Technique (intrinsic) limitations

  • No information regarding tissue architecture or presence/absence of fibrosis.
  • A transtracheal wash is a blind procedure and may not be representative of the lower airways.
  • BAL procedure, when blindly performed, may miss focal lesions.
  • Pathology/neoplasia that has not eroded alveoli/small bronchioles will not exfoliate into lumen.
  • Fine needle aspiration of lung parenchyma carries a significantly greater risk but may be necessary in poorly exfoliative lesions that do not involve the bronchial tree.
  • Total and differential cell counts in BAL fluid often differ between lung segments in cats with lower respiratory disease, and caution is warranted when using a single BAL cytology to define the inflammatory response in cats with spontaneously occurring lower respiratory tract disease.
  • Cytology cannot distinguish between bronchial asthma Allergic bronchitis and eosinophilic/chronic bronchitis Chronic bronchitis. (Asthma includes airway hyper-responsiveness and reversible bronchoconstriction - only detected by pulmonary function testing. Chronic bronchitis is characterized by airway inflammation and excessive mucus production - leading to irreversible narrowing of the airways).

Technician (extrinsic) limitations

  • Oropharyngeal contamination when sampling via endotracheal tube; some may occur with endoscopic sampling.
  • Hypotonic wash solution may cause cell lysis - use isotonic saline.
  • Hemorrhage associated with poor scope technique.

Result Data

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Further Reading

Publications

Refereed papers

  • Recent references from VetMed Resource and PubMed.
  • Ybarra W L, Johnson L R, Drazenovich T L et al (2012) Interpretation of multisegment bronchoalveolar lavage in cats (1/2001-1/2011). JVIM 26, 1281-1287 PubMed.
  • Padrid P A, Feldman B F, Funk K et al (1991) Cytological, microbiological, and biochemical analysis of bronchoalveolar lavage fluid obtained from 24 healthy cats. Am J Vet Res 52(8), 1300-1307 PubMed.

Other sources of information

  • Raskin R E, Meyer D J (2015) Canine and Feline Cytology: a colour atlas and interpretation guide. 3rd edn. Elsevier.
  • Valenciano A C, Cowell R L (2014) Diagnostic Cytology and Hematology of the Dog and Cat. 4th edn. Elsevier.


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