Bronchoalveolar lavage (BAL) sampling

Airway sampling is probably the most valuable diagnostic aid in respiratory medicine, allowing the identification of the primary cell type involved in pathological processes and offering the clinician the best opportunity to achieve a definitive diagnosis.

Practical Points of Airway Sampling

• Ideally samples should be obtained using a flexible endoscope after reviewing thoracic radiographs to identify the most likely productive sites for sampling.
• Do not radiograph after sampling as fluid that has not been aspirated will be seen on radiographs as an alveolar pattern.
• Material can be sometimes obtained without the assistance of an endoscope and, in those cases where anaesthesia is not possible, trans-tracheal or -laryngeal sampling is an option (tracheal/bronchial wash) - although cell retrieval is often disappointing.
• In preparation load five or six syringes with warm (non-bacteriostatic) saline; suitable volumes are approximately 0.5 ml/kg per syringe (+ ~ 2-3mls for catheter/endoscope dead space) to a max. of 20ml)
• To obtain a bronchoalveolar lavage (BAL) fluid sample, pass the flexible endoscope into the selected bronchus almost occluding it; then advance the endoscopic catheter (but keep within view)
• Flush the catheter with one syringeful of saline and immediately aspirate. Watch that the catheter is not occluded by the wall of the bronchus, the catheter/endoscope often needs to be moved back and forth to prevent this.
• Repeat this with 4 to 6 flushes - until a suitable sample is retrieved.

A ‘good’ lavage is indicated by:

• 50% of the sample volume being retrieved – usually by the 3 or 4 syringe (NB. the remainder is well absorbed by the lung).
• Foaming of the sample - indicating the presence of surfactant from the alveoli.
• Presence of cellular debris, mucus or a cloudy appearance.

Sample handling

• Preparation of top quality smears is vital for cell preservation - this must be done ASAP ( < 1 hour).
• Pool the collected material into 20ml universal pots and centrifuge
• Decant the supernatent (saline) with a pipette leaving the sediment and a small volume of saline in the pot.
• Gently mix (resuspend) the saline and sediment by drawing the sample in and out of the pipette.
• Place a spot of the BAL fluid sample containing cell material onto a number of glass slides, use the squash and pull apart method to spread cellular material and air dry rapidly by waving the glass slides in the air or using a hair-drier on a cold setting (this is vital for cell preservation).
• Further advice can be obtained from your specialist cytologist.
• Submit to an RCVS Specialist Clinical Pathologist (see RCVS Register!) such as Chris Belford of Cytopath (Tel: 01432 820888) or Nick Carmichael of CTDS (Tel: 0113 2870175)
• In the other aliquot, dip a swab (with transport medium) into the spot of sediment and submit for C&S

Interpretation of the cytologist’s report.

• A good BAL sample should be cellular with the presence of macrophages, indicating the lavage has reached alveolar level. An excessive amount of epithelial cells would indicate upper airway contamination. The presence of squamous cells or Simonsiellia would indicate oral contamination (note: this is important when interpreting any culture result)
• In normal animals macrophages make up the majority of cells recovered (these are normal and not inflammatory cells). There are usually some neutrophils and small numbers of lymphocytes, eosinophils.
• The presence of significant numbers of eosinophils support a diagnosis of pulmonary infiltration with eosinophilia, feline asthma syndrome or parasitism.
• Neoplastic cells support a diagnosis of neoplasia. 
• In non-specific inflammatory conditions the neutrophil is the predominant cell type, with variable numbers of macrophages and lymphocytes.
• The presence of red blood cells suggests bleeding into the airways, which may be due to the sampling procedure, FBs, lungworm or neoplasia (the cytologist can differentiate between fresh or chronic haemorrhage).
• A significant growth on culture should be associated with intra-cellular bacteria and absence of contamination on the cytology report.

Recommended reading Martin & Corcoran (2006) Notes on: Cardiorespiratory disease of the dog and cat, 2nd ed. Blackwell Science. ISBN 0-632-03298-7