Page 92 - ADULT-ONSET ASTHMA PREDICTORS OF CLINICAL COURSE AND SEVERITY

ADULT-ONSET ASTHMA – PREDICTORS OF CLINICAL COURSE AND SEVERITY
BIOMARKERS FOR DIAGNOSING ASTHMA: NOT QUITE A SMOKING GUN?
Up to 35% of asthma pa ents are smokers, which is comparable to the propor on of smokers in the general popula on 1. This large subgroup of asthma pa ents has par cularly poor clinical outcomes, with increased morbidity and mortality rates 1-3. Over the past decades, evidence has accumulated that smoking induces considerable altera ons in airway in ammatory processes in asthma pa ents 1, 2. Not surprisingly, exhaled nitric oxide (FeNO) 4 and blood eosinophils 5, both biomarkers of eosinophilic airway in amma on, are substan ally di erent in asthma pa ents who smoke, compared to those who do not. Smoking also induces resistance to cor costeroid treatment 6, which is the mainstay of asthma therapy. This raises the ques on whether the op mal strategy to diagnose and manage asthma pa ents is the same for smokers and non-smokers.
In this issue of Clinical and Experimental Allergy, Giovannelli and colleagues report on an evalua on of the associa on between FeNO or blood eosinophils and allergic asthma 7. This study addresses an important, yet so far insu ciently inves gated topic: whether or not the associa on between these biomarkers and allergic asthma is similar in the smoking and non-smoking popula on.
In a large cross-sec onal survey including 1,607 pa ents in the age range of 40 to 64 years selected from the general popula on, Giovannelli and colleagues found that FeNO and blood eosinophils were associated with a diagnosis of allergic asthma in never and former smokers, but not in current smokers. In a mul variate model, non-smoking pa ents with allergic asthma had much higher FeNO levels and blood eosinophil counts, compared to non- smoking individuals without allergic asthma. However, in the subgroup of current smokers no such di erences were observed.
The authors made an a empt to quan fy the poten al clinical value of FeNO and blood eosinophils in dis nguishing between pa ents with and without allergic asthma. For the group as a whole the diagnos c accuracy appeared to be far from perfect, whereas it seemed non-exis ng in the subgroup of smokers.
Interes ngly, these ndings di er from those in a previous study that evaluated the ability of FeNO to diagnose asthma in 282 pa ents with asthma-like symptoms. Overall, the diagnos c accuracy was equally mediocre, but not signi cantly di erent between never-smokers, ex- smokers and current smokers 8. Whether these ndings di er due to chance, heterogeneity in the popula ons studied, or varying methods between the studies, is open for debate.
Despite the careful design and impressive sample size, the study by Giovannelli and colleagues has a few limita ons. Only 14 pa ents out of 294 current smokers (5%) were diagnosed with allergic asthma. This small number has certainly limited the power to detect signi cant associa ons with FeNO levels and blood eosinophil counts in this subgroup. In addi on, the authors relied on a reference standard of self-reported physician-diagnosed asthma. Yet, serious concerns exist about the accuracy of self-reported asthma 9. Nevertheless,
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