British Lung Foundation researchers at Imperial College have discovered that testing the phlegm, fluid and gases breathed out by children with severe asthma is an effective way of monitoring inflammation.
The researchers suggest that the tests could be introduced to help manage asthma more effectively.
Children who have severe asthma take courses of steroids to control their symptoms but this research shows that careful monitoring using this new test could reduce the use of steroids by a third.
The study involved 55 children aged between seven and 17 years over a period of three years.
Airway inflammation is a characteristic of asthma but monitoring currently consists of lung function testing, which does not measure airway inflammation.