Combined Tests Provide Better Asthma Diagnosis

Fraction of exhaled nitric oxide (FENO) and blood eosinophil-count values, markers of local and systemic eosinophilic inflammation, respectively, are increased in asthmatic patients.

Measurement of the concentration of exhaled nitric oxide is today a routine clinical method for determining the degree of steroid-sensitive inflammation in the airways in asthma and for many years, a count of eosinophil granulocytes in the blood has also been used to support a diagnosis of asthma.

Scientists at Uppsala University (Sweden) measured FENO and eosinophil values in 12,408 subjects aged 6 to 80 years from 2007 to 2008 and from 2009 to 2010. Current wheeze and asthma diagnosis, as well as asthma attacks and asthma-related emergency department (ED) visits within the last 12 months, were assessed by means of questionnaires.

The FENO values were measured with the NIOX MINO electrochemical analyzer (Aerocrine AB; Solna, Sweden) at an expiratory flow rate of 50 mL/second. Blood differential counts were performed by using the automated HmX hematology analyzer (Beckman Coulter; Fullerton, CA, USA). The following cutoffs for eosinophil values were used: less than 300 cells/mm³ to define normal values; 300 cells/mm³ or greater but less than 500 cells/mm³ for intermediate values and 500 cells/mm³ or greater for high values, as this is the limit for defining eosinophilia.

The scientists were able to determine that the association between FENO and blood eosinophils was very weak. Instead, they observed that simultaneously elevated levels of the two markers, in a synergistic way, but independently of each other, increased the likelihood of individuals reporting, for example, asthma symptoms or asthma attacks in the last year. The results supported their hypothesis that the two markers represent two different inflammation processes.

Kjell Alving, PhD, a professor at the Department of Children's and Women's Health, Uppsala University, and a senior author of the study said, “We therefore propose that both of these measurements be carried out in combination in order to better understand the inflammation in asthma patients. They thus constitute a better platform for selecting the proper treatment for these patients.” The study was published in the October 2013 issue of the Journal of Allergy and Clinical Immunology.

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Uppsala University
Aerocrine AB
Beckman Coulter