Simultaneously elevated FeNO and blood eosinophils relate to asthma morbidity in asthmatics from NHANES 2007-12

Fraction of exhaled nitric oxide (FeNO) and blood eosinophil (B-Eos) count are biomarkers for type 2 inflammation. However, they signal different inflammatory pathways. Simultaneously elevated, they are related to more asthma events in a general population and among younger asthmatics.

To investigate if simultaneously elevated FeNO and B-Eos relate to asthma outcomes and lung function among subjects with asthma at a wide age span, and how different cut-offs for the markers affect these relations.

FeNO, B-Eos and forced expiratory volume in 1 second (FEV₁ ) were assessed in 1419 subjects with asthma, aged 6-79 years old, from the National Health and Nutrition Examination Survey (NHANES) 2007-12. Elevated levels were defined as FeNO ≥20 p.p.b. for children <12 years and ≥25 p.p.b. for subjects ≥12 years and B-Eos count ≥300 cells/μL. Additional analyses were performed for the cut-offs FeNO >35/30 and >50/35 p.p.b., and for B-Eos ≥400 and ≥ 500 cells/μL, as well as for different age subgroups (6-17, 18-44, >44 years old). Asthma events during the past year were self-reported.

Subjects with simultaneously elevated FeNO and B-Eos compared with normal levels of both markers had a higher adjusted odds ratio (aOR (95%CI)) for having FEV₁ <80% of predicted (2.15 (1.28-3.59), wheeze disturbing sleep (1.88 (1.27, 2.78)) but did not differ regarding asthma attacks past year. Elevated B-Eos, but not FeNO, was related to higher aOR for asthma attack (1.57 (1.14, 2.18) or emergency room (ER) visit due to asthma (1.88 (1.33, 2.64) when elevated FeNO and elevated B-Eos were studied as independent predictors.

Simultaneously elevated FeNO and B-Eos related to reduced lung function in asthmatics, wheezing symptoms, but not to a history of asthma attacks. Asthma attacks and ER-visit due to asthma were related to increased B-Eos levels.