In older children and adults the patient can be asked to cough up a sample of sputum. However, younger children under 6 years of age are usually unable to caugh up sputum to examine, as sputum is swallowed. If a sputum sample is needed in a child, it is easier to take a sample of gastric fluid which contains swallowed sputum. The gastric aspirate is best collected early in the morning before the first feed, the child having been nil per mouth for 6 hours. As gastric fluid is highly acid, 4% sodium bicarbonate in an equal volume to the gastric aspirate should be added to the specimen to neutralize the acid. Otherwise the TB bacilli will be killed before they can be cultured.
As children usually cough up or swallow far fewer TB bacilli than adults do, positive cultures are less common in children. Therefore, diagnosing tuberculosis in children is often done without obtaining a sputum sample.
A useful method of promoting coughing and sputum collection in a child can be performed before a meal. A puff of inhaled bronchodilator is given using a spacer followed 10 minutes later by 5 ml hypertonic saline (5% saline) also by nebuliser. This is followed by chest physiotherapy to loosen the mucus and promote coughing.