bronchoalveolar lavage

Bronchoalveolar lavage (BAL) is a gentle wash of one small region of lung to collect what lives deep in the air sacs. During bronchoscopy the scope is wedged into a chosen sub-segment of airway, sterile salt water is squirted in to flood the surrounding alveoli, and then suctioned back. The recovered fluid carries with it a sample of the cells, microbes and proteins from that part of the lung — like rinsing a sponge and studying the rinse water.

That returned fluid is sent for analysis: cell counts and types (for example a predominance of certain immune cells), stains and cultures for bacteria, fungi and viruses, and tests for unusual material. The makeup of the washings can point toward infection, certain interstitial lung diseases, alveolar haemorrhage, or specific conditions with characteristic findings.

BAL samples the air-space contents and surface cells rather than solid tissue, so it complements but does not replace a biopsy when actual lung architecture must be examined. It is especially valuable in patients with weakened immune systems and diffuse lung shadows, where identifying an opportunistic infection quickly guides treatment. It is low-risk and adds little time to a routine bronchoscopy, though it can cause a transient cough, fever or brief dip in oxygen.