Biomarkers are substances, such as proteins and enzymes that can be used as objective indications of medical conditions that can be measured specifically and reproducibly. These medical findings differ from medical symptoms, which are limited to the signs of health or illness that can be perceived by the patients themselves. 

A known problem with lung diseases such as COPD and asthma is that the illness often starts with changes in the small airways, but there are no quantitative or non-invasive methods to study these changes. The same applies to the diagnosis of more severe forms of asthma that just affect the small airways. Traditional diagnostic methods like X-rays or lung function tests are deemed to provide limited information, often leading to only being able to determine exactly what disease the patient is suffering from at a relatively advanced stage.

Research in the area is increasingly geared towards searching for specific biomarkers for various diseases. The methods used to date in research are either not quantitatively reliable or so distressing to the patient that they are difficult to use repeatedly and if suffering from a serious condition.