Bronchial tracheal wash: cytology

Bronchoalveolar lavage BAL • Tracheal aspiration • Tracheal wash TW.

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  • 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 dog by a transtracheal wash (percutaneously), or under anesthesia through an endotracheal tube, or by endoscopy.
  • Used where there is clinical signs and radiographic evidence of tracheal or bronchoalveolar disease to evaluate pathology, to assist in therapeutic choices.



  • Investigation of chronic cough that may be persistent, intermittent or episodic.
  • Investigate abnormal respiratory rate (tachypnea) or effort (dyspnea) in stable patients.
  • Harsh lung sounds, including inspiratory crackles or expiratory wheezes.
  • Labored respiration, abdominal breathing in stabilized patients.

In combination

  • Thoracic radiography : if evidence of pulmonary, bronchial or alveolar disease.
  • Bronchoscopy: in evaluation of bronchopulmonary disease (not always possible, eg small dog breeds).
  • Bronchial biopsy/brush: when lesions are visualized on bronchoscopy.
  • Percutaneous fine needle lung aspiration might be indicated in patients with large focal lesions or less commonly diffuse disseminated pulmonary disease [Lung: bacterial pneumonia]. All potential contraindications should be eliminated before attempting this procedure.
  • Histopathology and specific viral isolation techniques.
  • Fecal examination with Baermann technique or zinc sulfate flotation to identify parastic larvae or ova.
  • Serology for heartworm [Canine cardiopulmonary dirofilariasis].

Result data

Normal (reference) values

Normal (reference) values

  • Standard cytological findings are well documented, but considerable variation can occur depending on the specific method of collection, the level at which the respiratory system is being sampled, and variation in a clinician's technique and competency. These factor must be borne in mind during cytological evaluation to achieve an accurate diagnoses.

Tracheal wash

  • Ciliated columnar or cuboidal epithelial cells predominate.
  • A few alveolar macrophages.
  • Rare neutrophil.
  • Rare goblet cell.
  • Small amount of mucus.
  • Oropharyngeal contamination more likely compare to BAL.
  • Presence of superficial squamous epithelial cells that may be superimposed by a mixed population of bacteria including Simonsiella indicate oral contamination.

Bronchoalveolar lavage

  • Alveolar macrophages predominate.
  • Differential cell count in a healthy dog includes 70-80% macrophages, <5% neutrophils, 6-14% lymphocytes, 1-2% mast cells, <5% eosinophils.
  • Erythrocytes and epithelial cells hould only be present in low numbers.
  • Low numbers of goblet cells.
  • Small amounts of mucus.

    Starch granules, pale refractile hexagonal structures (glove powder) are contaminants.

Abnormal values

Neutrophilc (suppurative) inflammation


  • Neutrophils predominate and are usually non-degenerate, but can be degenerate.
  • Aspiration pneumonia .
  • Neutrophils can predominate in chronic allergic disease.
  • Neoplasia, eg lymphoma - lymphoblasts .
  • Repeated bronchial lavage - the actual previous wash will increase the number of neutrophils seen in subsequent washes if performed within a few days.

Infectious (septic)

  • Bacterial infection - many degenerate neutrophils and intracellular bacteria (especially if seen on direct smears made at the time of sampling) support the diagnoses of bacterial infection.
  • Viral infection - neutrophils and small lymphocytes (distemper and adenovirus ).
  • Protozoal infection , Toxoplasma gondii [Toxoplasmosis].
  • Parasitic worms - inflammation can be neutrophilic, eosinophilic or mixed. Filaroide's larvae incite suppurative rather than eosinophilic inflammation.
  • Foreign bodies - numerous neutrophils, mixed population of bacteria, macrophages, +/- plant materials [Airway foreign body].
Non-suppurative/chronic inflammation
  • Foamy active macrophages predominate with fewer neutrophils, reactive lymphocytes, plasma cells, and some eosinophils.
  • Curschmann's spirals - tight coils of inspissated mucus formed in small bronchioles.
  • Granular material in macrophages may be haemosiderin, mucin or carbon.


Infectious etiologies(septic)

Eosinophilic inflammation

  • May include increased eosinophils, macrophages and neutrophils.
  • >10% Eosinophils suggest a hypersensitivity, parastic or infiltrative process may be involved.
  • Mast cells may be present.
  • Low numbers of lymphocytes and plasma cells may be present.
  • Hypersensitivity due to inhaled allergens.
  • Parastic infection including lungworms, Filaroides spp (dead/dying worms), Capillary aerophilia.
  • Can be seen with bacterial and fungal infection.
  • Pulmonary infiltrate with eosinophils (pulmonary eosinophilic gramulomatosis).
  • Paraneoplastic syndromes and tumor-associated tissue eosinophilia, eg MCT, lymphoma.

Hemorrhagic inflammation

  • Increased erythrocytes, erythrophagia and inflammatory cells.
  • Cute can be distinguished from procedural (iatrogenic) hemorrhage if eryhrophagia is present on direct smears made at time of sampling.
  • Chronic is characterized by the presence of erythophagia combined with black particles within macrophage cytoplasm interpreted to be haemosiderin.
  • Haemosiderophages (iron-laded macrophages) can be identified with special stains (Perl's or Prussian blue ).
  • Haemotoidin (bright yellow rhomboid shaped crystals) indicates hemorrhage under hypoxic conditions.
  • Can be seen with trauma, foreign body, coagulopathy, neoplasia, congestive heart failure, pulmonary hypertension or thromboembolism.

Neoplastic cells

  • Evidence of primary or metastatic neoplasia in a TW or BAL is rare because of their interstitial location.
  • Metastatic neoplasia is more common than primary respiratory tract neoplasia.
  • Carcinoma is the most common neoplasia but others including lymphoma can occur.
  • Hyperplastic, dysplastic or reactive respiratory epithelium may be misinterpreted as neoplastic. Therfore if neoplasia is suspected cytologically, it should be confirmed with a biopsy.

Errors and Artifacts

  • Failure to detect cause of pulmonary disease.
  • Contamination with oral flora.
  • Unsuccessful wash - low cell yield.
  • Cells trapped in large mucus plugs and no squash preparations at the time of collection can result in a non-representative sample.
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