Testing the breath and phlegm of children with severe asthma could reduce their dependence on steroids, researchers at Imperial College London have suggested.
They said that the tests could help spot early the signs of worsening asthma, allowing it to be brought back under control.
In addition, the tests cut the use of oral steroids by nearly a third over a three-year period.
Asthmatic kids are given a steroid inhaler to help them control the asthma, but if this is not working, then higher doses of steroid are given in tablet or medicine form to get it back under control, and cut the risk of serious attacks or hospitalisation.
However, physicians try to avoid these 'rescue steroids' because if used too often, it can cause side effects such as growth problems.
The tests look for signs of increasing lung inflammation - the presence of cells called eosinophils in the sputum, and higher than usual levels of nitric oxide gas in the breath.
These signs could appear before the symptoms of asthma themselves changed.
For the study, researchers compared the progress of children assessed using symptoms and lung function tests - the conventional way - with a group given the sputum and breath tests.
In either case, if doctors judged that the asthma was likely to be worsening, they increased the dose of the steroid inhalers used by the children.
If this failed to improve matters, oral steroids were used.
Researchers found that, on average, there was a 29 percent reduction in the number of courses of oral steroids used by the children in the sputum and breath test group.
A third of the children in that group did not need any courses of oral steroids, compared with 12.5 percent of those in the conventionally monitored group.
"It's a much more efficient way of making sure children with severe asthma get the treatment they need," BBC quoted Professor Andrew Bush, who led the research, as saying.
Co-author Dr Louise Fleming said that the objective of the study was not only to decrease the number of severe attacks, but also to make sure that children were not on too high a dose of inhaled steroids all the time.