ATS Guidelines Offer FENO Interpretation Recommendations

September 9, 2011 — New guidelines from the American Thoracic Society (ATS) provide clinicians with a user-friendly reference not just for the use of fractional exhaled nitric oxide (FE_NO), but also, importantly, for interpretation of FE_NO levels in the context of varying clinical settings.

In the management of airways diseases such as chronic asthma, FE_NO measurement offers an important advantage vs other conventional tests, such as reversibility or provocation tests involving forced expiratory volume in 1 second, which are only indirectly associated with airway inflammation, according to Raed A. Dweik, MD, chair of the guideline writing committee and professor of medicine and director of the Cleveland Clinic's Pulmonary Vascular Program in Cleveland, Ohio.

"Properly employed, FE_NO can offer added advantages for patient care," Dr. Dweik said in an ATS news release. "It can detect eosinophilic airway inflammation, determine likelihood of corticosteroid responsiveness, monitor airway inflammation to determine the need for corticosteroid, and reveal patient non-adherence to corticosteroid therapy."

However, use of FE_NO is currently only sporadic, and although the measurement for testing is standardized, interpretation of results in the clinical setting is not.

The guidelines, which are published in the September 1 issue of the American Journal of Respiratory and Critical Care Medicine, represent the writing committee's goal to provide a better framework for interpretation, Dr. Dweik noted.

"The guidelines provide a practical approach to use and interpret FE_NO in daily clinical practice, and will standardize the approach by which physicians and other healthcare providers utilize FE_NO to manage patients with airway disease," he continued.

Diagnostic Uses

In the use of FE_NO for diagnosis, for instance, the writing committee recommends use of the test to:

Diagnose eosinophilic airway inflammation;
Determine the likelihood of corticosteroid responsiveness in individuals with chronic respiratory tract symptoms possibly arising from airway inflammation;
Support the diagnosis of asthma in situations where objective evidence is needed; and
Monitor airway inflammation in patients with asthma.

Recommended Cutoff Values

The committee also sets forth the following recommended cutoff points for clinical decision making:

An FE_NO level of less than 25 ppb (< 20 ppb in children) indicates that eosinophilic inflammation and responsiveness to corticosteroids are less likely;
An FE_NO level of more than 50 ppb (> 35 ppb in children) indicates that eosinophilic inflammation and, in symptomatic patients, responsiveness to corticosteroids are likely; and
FE_NOvalues between 25 and 50 ppb (20 - 35 ppb in children) should be interpreted cautiously with reference to clinical context.

In addition, the guidelines recommend that clinicians consider FE_NO increases of 20% or more for values of more than 50 ppb, or 10 ppb more for values less than 50 ppb, to represent a significant increase from one visit to the next. Conversely, reductions of 20% (or 10 ppb) should indicate a significant response to anti-inflammatory therapy.

The committee notes that changes in FE_NO, even if the measurements do not achieve normal values, may be particularly useful indicators in the assessment of patients with asthma who have more than 1 factor contributing to respiratory tract symptoms, such as obesity or anxiety. Assessment of changes in FE_NO levels may also be beneficial before and after allergen inhalation challenge testing.

Importantly, to better understand the broader implications of FE_NO levels, the committee calls for more research into the interpretation of measurements in different clinical settings.

"Inclusion of FE_NO as an endpoint in clinical trials would be very helpful in understanding the role of FE_NO in monitoring response to therapy," the committee writes. "Furthermore, FE_NO measurement in large population-based studies like the National Health and Nutrition Examination Survey (NHANES) would provide more information on normative values."

Some of the study authors have disclosed various financial relationships with Critical Therapeutics, Genentech, Merck, GlaxoSmithKline, Sepracor, Aerocrine and Apieron (makers of FE_NO measuring equipment), Asthmatx, Hope Pharmaceuticals, Ikaria, AstraZeneca Sweden, and/or Aerocrine AB. One of the study authors has received royalties from book publishers.

Am J Respir Crit Care Med. 2011;184:602-615.

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