FENO and B-Eos complement each other as asthma biomarkers

Research indicates that fraction of exhaled nitric oxide (FENO) and blood eosinophil count (B-Eos) values can independently predict asthma diagnosis and attacks.

However, the study authors, led by Andrei Malinovschi (Uppsala University, Sweden), found evidence that the two markers reflect distinct elements of the inflammatory process, with only a weak correlation in their levels.

“Our data support the view that these 2 markers cannot be used interchangeably but should be used in combination,” they therefore conclude.

The team analyzed data on 12,408 participants in the US National Health And Nutrition Examination Survey.

They observed that increasing levels of FENO and B-Eos both correlated with increasing rates of current asthma and wheeze in the past 12 months, as well as respectively with asthma attacks and asthma-related emergency department visits in the past 12 months.

For example, individuals with high FENO values (≥35 ppb if <12 years old; ≥50 ppb if ≥12 years old) had an asthma rate of 22.9% compared with 7.1% in those with normal FENO values (<20 ppb if <12 years old; <25 ppb if ≥12 years old).

Meanwhile, in patients with high B-Eos values (≥500 cells/mm³) the rate of asthma was 18.1% versus 6.8% in those with normal values (<300 cells/mm³).

But when the researchers combined the two markers, they found they had additive value in predicting asthma outcomes; the prevalence of current asthma was 6.2% among those with normal FENO and normal B-Eos values compared with 33.3% in the group with both high FENO and high B-Eos values.

Having intermediate or high FENO levels and intermediate or high B-Eos levels was independently associated with current asthma, wheeze, and asthma attacks but only intermediate or high B-Eos levels were independently associated with emergency room visits.

But, writing in the Journal of Allergy & Clinical Immunology, Malinovschi and colleagues note that there was only a weak correlation between the two biomarkers, with an explanatory value of only around 4%.

“This, together with the clear-cut additive effect of these markers on the risk for asthma, wheeze, and asthma attacks in our study, indicates that they represent 2 different inflammatory pathways with separate trigger mechanisms,” the team comments.

Writing in an accompanying editorial, Ian Pavord and Mona Bafadhel from the University of Oxford, UK, say the findings support the use of the markers as a less invasive way to measure eosinophilic airway inflammation than other methods, such as induced sputum.

“[I]t cannot be assumed that symptom control equals inflammation control. The clear implication is that for optimum control of inflammatory airway diseases, we need to move on from a strategy that seeks to suppress symptoms and normalized lung function to one that includes the extra goal of minimizing preventable risk, as indicated by blood eosinophilia, an increased FENO value, or both,” they conclude.

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