Glossary
Bronchoalveolar lavage (BAL).
Direct answer
Bronchoalveolar lavage is a sampling technique in which sterile fluid is instilled through a tube into a deep region of the lung and then aspirated back. The recovered fluid contains cells from the lung periphery and is used for cytological assessment of inflammation in the deep airways.
The distinction from a tracheal wash matters: a tracheal wash samples higher in the airway tree. The two samples often disagree because they describe different regions, so a tracheal sample does not replace deep lavage when the lower airways are the question. Macrophages, lymphocytes, neutrophils, mast cells and eosinophils are counted.
The sample comes from a single lung region. If the change is patchy it can be missed, which is why both lungs are sometimes sampled. In people, lavage is used mainly to investigate infection and interstitial disease; in the horse it is the central tool for characterising equine asthma.
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