Useful: in patients with suspected mycobacterial lung infection who are not able to expectorate sputum but are suspected of swallowing respiratory secretions. Particularly useful in children. This is not suitable for routine bacterial sputum culture and sensitivities.

Note induced sputum is preferable to gastric washings, if available. The patient should be nil by mouth from midnight, and samples collected first thing in the morning before breakfast. Insert the largest bore NG tube that is comfortable without lubrication (because it's bacteriostatic). Aspirate stomach contents: if less than 10mls of mucus is collected, then instill 10-20mls of sterile water (not saline) down the NG tube and quickly reaspirate before putting in specimen container. Collect 3 separate gastric washings this way on three consecutive days and transport to the laboratory quickly to avoid stomach acid breaking down the sample.