Experts outline biomarkers to measure asthma, highlighting eosinophil count and fractional exhaled nitric oxide levels.
Raffi Tachdjian, MD, MPH, FAAAAI, FACAAI: We talked about biomarkers to start this conversation and segment, to qualify the level of severity of asthma. And we’re going to wind down now and come full circle. Dr Siri, what is the role of biomarkers as you progress prognostically and follow your patients who are on biologics?
Dareen D. Siri, MD, FAAAAI, FACAAI: Thank you for asking me that because we’ve all been throwing out the word biomarkers without actually really defining them. The FDA defines biomarkers as something that we can objectively measure that really will give us a prediction in terms of health, disease, perhaps treatment response to a therapeutic, or even just an exposure. Specific to moderate and severe asthma, one of the big biomarkers we’re talking about is the eosinophil count, which is easily measured in a primary care office…. So thank you for doing a great job and getting a CBC [complete blood count] with differential before you refer them. We would love that. An eosinophil count greater than 150 [cells/µL] certainly can be indicative of type 2 inflammation. That is helpful, and that’s been borne out by some clinical studies that we talked about. And a count of 300 or greater has additional prognostic markers.
Fractional exhaled nitric oxide [FeNO] is also really important in terms of that correlation. FeNO may not be as available for a primary care audience, but certainly, for allergist immunologists, we measure it very frequently. And this could be indicative of airway inflammation and certainly interleukin-13 activity. Someone with a FeNO level of 20 or 25 ppb or greater is considered inflamed and could benefit from additional treatment.
You can think of that also in other pulmonary function testing such as spirometry. We can use FEV1 [forced expiratory volume in first second of expiration] as a measure. Also, impulse allometry, which is making a comeback, can be used as a measurement in terms of increased risk.
When we use biomarkers, we can also think about immunoglobulin…or some of the other blood work that we might check. Those don’t have as much of a predictive outcome as eosinophils and FeNO, but they certainly still would be helpful. Lastly, there may be something such as genetic biomarkers. This is becoming more and more advanced as time goes on. And I think at some point we will be able to direct treatment in terms of those genetic factors. That can be very helpful. In terms of the biomarkers, what do they do for us? Certainly, they can help us direct the right therapy. They can help us monitor the patient. They can help us predict the severity of the disease. I do think that we should follow this along because it’s going to be really helpful for us to discover more biomarkers that may be predictive for our patients.
Transcript edited for clarity