Transtracheal Wash and Bronchoalveolar Lavage: Airway Sampling in Dogs

Airway sampling can provide additional information when evaluating lower respiratory tract disease. Transtracheal wash (TTW) and bronchoalveolar lavage (BAL) allow cytological and, where applicable, microbiological assessment of airway material. Their interpretation is most useful when integrated with the clinical and imaging findings. 

What Transtracheal Wash Samples 

Tracheal wash aspiration is a minimally invasive procedure that predominantly samples the larger airways while also obtaining some material from the lower airways and alveoli for cytological and culture analysis. Mucociliary clearance and the cough reflex contribute to sample extraction^1,2. 

Cytological interpretation should include estimated cellularity, differential cell counts, and morphological description of the cells encountered². 

In clinically normal animals, tracheal aspirates contain predominantly alveolar macrophages, along with respiratory epithelial cells, lymphocytes at 5–14 percent, neutrophils at 5–8 percent, eosinophils at less than 5 percent, rarely mast cells at less than 2 percent, and mucus². 

Interpreting Abnormal TTW Cytology 

Neutrophilic or mixed inflammation is the most common abnormality identified on TTW cytology in dogs with spontaneous respiratory disease². 

Neutrophilic inflammation is observed in the majority of dogs with bacterial infection, and intracellular bacteria and degenerative changes in neutrophils may also be seen in some dogs². 

The source also reports characteristic cytological findings in specific respiratory conditions. In dogs with chronic bronchitis, TTW cytology showed increased cellularity, a moderate increase in neutrophils, mucus, and sloughed hyperplastic epithelial cells^2,3. 

In dogs with eosinophilic bronchopneumopathy, severe eosinophilia of 50–60% was reported in tracheal wash cytology. This is a reported clinical finding and should be interpreted in conjunction with the overall clinical presentation². 

What BAL Adds² 

Bronchoalveolar lavage is described as an inexpensive, minimally invasive method for cytological and microbiological examination of the lower airways. 

Alveolar macrophages are the predominant cell type in normal canine BAL fluid. The fluid is highly cellular and permits high-quality cytological specimen preparation. Infectious organisms, including bacteria and fungi, are more commonly identified in BAL cytology than in tracheal wash specimens. 

Normal BAL fluid cytology consists of alveolar macrophages at 70–80 percent, lymphocytes at 7–12 percent, neutrophils at 5–10 percent, eosinophils at 6–11 percent, mast cells at 1–2 percent, and epithelial cells at 1–2 percent. 

Classifying BAL Inflammation² 

Based on differential cytology, BAL fluid can be categorized as normal, lymphocytic when lymphocytes exceed 50%, neutrophilic when neutrophils exceed 50%, eosinophilic when eosinophils exceed 50%, or mixed inflammation. 

Practical Clinical Insight 

The sampling site matters when interpreting cytology. Transtracheal wash predominantly evaluates larger airways, whereas BAL provides cytological and microbiological examination of the lower airways. 

Nasal swab and sputum cultures are described as less reliable because of contamination with normal nasal and oropharyngeal microflora. Bronchoscopy can assist in evaluating tracheobronchial collapse, intraluminal masses, strictures, traumatic injuries, pneumonia, and chronic bronchitis. 

Where airway sampling is performed, cytology should therefore be assessed systematically, cellularity, differential counts, and morphology, rather than relying on a single inflammatory finding. 

References 

1. Graham AM, Tefft KM, Stowe DM, Jacob ME, Robertson JB, Hawkins EC. Factors associated with clinical interpretation of tracheal wash fluid from dogs with respiratory disease: 281 cases (2012-2017). Journal of veterinary internal medicine. 2021 Mar;35(2):1073-9. https://academic.oup.com/jvim/article-pdf/35/2/1073/66651533/jvim16052.pdf 

2. Kaur J, Singh S. Respiratory diseases and their diagnosis in dogs: A review. Indian Journal of Animal Research. 2022. https://arccjournals.com/journal/indian-journal-of-animal-research/B-4994 

3. Kaur J, Singh S, Gupta K, Anand A. Diagnosis of canine chronic bronchitis using radiography and tracheal lavage. Indian J. Vet. Med. 2021;41(2):27-33. https://isvm.org.in/backend/web/uploads/Paper5d.pdf