Table 4.

Comparison of selected biosamples collected from the respiratory tract. Described criteria relate to collection procedure and RNA quality/quantity.

	EBC	SPUTUM	BALF/BB
Invasiveness	None	Low (higher with induction)	High
Risk of bacterial contamination	Medium	High	Medium/high (BALF)
RNA abundance	Very low	Low/medium	High
Equipment and staff	Dedicated collection, devices and trained personnel	Collection pan and trained personnel (induction)	Specialised equipment (bronchoscope) and highly trained personnel
Time of sample collection	10–30 min	Depending on the expectoration capacity	Around 2 h