Table 1. Airway fluid sampling.

Typical approaches for sampling airway fluids.^1–13

Approach	Volume recovered	Protein concentration and/or type	Limitations of approach
Bronchoalveolar lavage	50–100 ml	0.05–1.5 μg/pL Plasma proteins abundant in the presence of airway inflammation	Method is invasive; primarily for research application No consensus for recovery control or normalization
Induced sputum	0.5–3.0 ml of sputum + saline	Sample is mucous-rich, which may interfere with downstream analysis	Method samples proximal airway fluid; contamination with saliva can interfere with airway sampling
Nasopharyngeal aspirate	Protocol dependent	Mucous rich	Samples upper respiratory tract- regional
EBC	1 ml/5–15 min collection	No cells are obtained Cytokines IL-8, IL-1b, TNF, IL-10 detectable Gases and metabolites	Dilution controls needed Samples airway lining fluids and proteins, no cells recovered
Plasma	10–100 ml	Wide dynamic range in the milligram per milliliter range, requires depletion approaches	Not fully representative of airway proteins Large dynamic range of proteins complicates analysis