Asthma is an inflammatory disease of the airways. The inflammation makes your airways sensitive, or irritable. Sensitive airways react to allergens and irritants by becoming narrow, or obstructed, which limits airflow.1
To treat your asthma, your doctor may use inflammatory biomarkers. Biomarkers are values that can be measured in a lab that reveal things about a disease. Biomarkers can give your doctor a better understanding of your asthma and help them decide on more targeted treatments.2
What are inflammatory biomarkers for asthma?
Eosinophils are inflammatory cells with an important role in asthma. About half of people with asthma have high eosinophils. Also, people with more eosinophils tend to have more severe asthma. Testing biomarkers for asthma often depends on measuring quantities of eosinophils.1,3
Examples of biomarkers of inflammation for asthma include:2,4
- Exhaled nitric oxide, a measure of the amount of nitric oxide in your breath, which is linked to increased eosinophils in the airway
- The percentage of eosinophils in the mucus from your lungs
- The percentage of eosinophils in a blood sample
Measured exhaled nitric oxide is a more common test your asthma specialist may perform. Blood and mucus eosinophils are mainly measured for research purposes. This information is used for studies that are trying to define different types of asthma and for studies of new treatments. More information is needed about how to use the results of these tests in everyday practice.1,5
Another inflammatory biomarker that is still being researched is called periostin. Periostin is a protein made by the cells in your airway. People with asthma may have higher levels of periostin. However, the research on asthma and periostin is in the early stages, and testing is not yet common.2,4
Exhaled nitric oxide (FeNo)
Many people with asthma have high levels of nitric oxide in their breath. Increased nitric oxide is linked with increased eosinophils in the airway. When people with high levels of nitric oxide take inhaled corticosteroids, their asthma usually gets better. For this reason, the American Thoracic Society recommends measuring fractional exhaled nitric oxide (FeNO).1,6
The FeNO test is not invasive and can be done at your allergist’s office. It is performed using a device with a monitor and a mouthpiece. First, you inhale filtered air through the mouthpiece until your lungs are full. Then you exhale into the mouthpiece at a constant rate for 10 seconds. The results are available in 1 minute.7
How are the results of FeNO testing used?
The results of the test are given in parts per billion (ppb). Depending on the ppb measured, your doctor may adjust your medicine. People with higher FeNO tend to respond well to inhaled corticosteroids. However, inhaled corticosteroids may not work as well for people with a lower FeNO.6
FeNO can also be used to measure changes in inflammation over time. Additionally, some studies have shown that FeNO measurements can help your doctor know whether you need more or less medicine.1
More research is about FeNO testing is needed. Researchers want to figure out how factors like age, smoking, and the use of medicines influence FeNO test results. Besides asthma, high FeNO may be a sign of bronchitis, hay fever, and other allergic diseases.2,8
FeNO cannot be used alone to diagnose asthma. However, if a person has other signs and symptoms of asthma, high FeNO supports the diagnosis.1
The number of eosinophils in mucus from the lungs is linked with asthma severity and response to treatment. This test is done in research studies more often than in everyday practice. The test requires highly trained staff to perform it.1
The eosinophils test involves coughing up mucus from your lungs. You inhale a salt spray, which draws water into your airways. The extra water in your airways thins out the mucus and makes it easier to cough up. The test takes between 5 and 20 minutes. If 3 percent or more of the cells in your sample are eosinophils, you have high levels of eosinophils.1,5
How are the results of mucus eosinophil testing used?
More research is needed on how to use the results of this test in everyday practice. In studies, adjusting treatment based on eosinophil levels has been helpful. People who were treated until their mucus eosinophil levels were normal had better control of their asthma, fewer asthma attacks, and fewer hospitalizations.1
Blood samples are easier to collect than lung mucus samples. Asthma cannot be diagnosed from the level of eosinophils, but the results can provide other helpful information. High levels of eosinophils may indicate you are at a higher risk for severe asthma. The levels of eosinophils in the blood may also predict how your body will respond to certain treatments.2,4
Were inflammatory biomarkers used in your asthma diagnosis? Share your experience in the comments below.