Page 168 - ADULT-ONSET ASTHMA PREDICTORS OF CLINICAL COURSE AND SEVERITY

ADULT-ONSET ASTHMA – PREDICTORS OF CLINICAL COURSE AND SEVERITY
Secondly, in our study and other studies there is no perfect correla on between sputum and blood eosinophilia or FeNO for example. Probably slightly di erent underlying mechanisms lead to uctua ons in the levels of these markers. This increases the diagnos c uncertainty of a given biomarker.
Thirdly, nding the op mal cuto values is always a ma er of debate and results di er strongly between several studies.13 De ning cufo values for biomarkers should depend on the purpose of the marker: either exclude or con rm a certain condi on. This method was used in Chapter 4.
Finally, an important ques on is whether the biomarker under inves ga on correlates with the disease outcome and response to therapy. For example, in Chapter 8 we showed that blood eosinophilia in non-smokers correlates with frequent exacerba ons, as previously shown.21 Several studies have addressed response to therapy: for example FeNO or exhaled breath have been shown to predict response to inhaled cor costeroid treatment.22, 23
Despite the several issues associated with biomarker use, biomarkers are de nitely clinically useful in adult-onset asthma. In an era where we are ge ng towards precision medicine for more and more diseases, it would be very old fashioned to consider all asthma pa ents having the same disease (both clinically and biologically). Several studies have described di erent asthma phenotypes, also based on in ammatory markers like sputum eosinophils. Development of novel targeted therapies stresses the need to use biomarkers for selec on of pa ents who will bene t most. Finally, monitoring disease ac vity is an important aspect of biomarker use which can be used to adjust treatment dose in an early stage and prevent deteriora on of the disease. Biomarker use, with observance of its limita ons, will improve care for our pa ents. Hence we should focus on the possibili es of the available biomarkers rather than the uncertain es.
DIFFERENT BIOMARKERS FOR EOSINOPHILIA IN DIFFERENT CLINICAL
ASTHMA PHENOTYPES?
Apart from in ammatory phenotypes, several clinical asthma phenotypes have been described over the past years.24 For instance asthma associated with obesity, gender, smoking or atopy. It is proposed that there are di erent mechanisms leading to the asthma and in amma on in these respec ve phenotypes. However, in all phenotypes, a propor on of one third to half of the pa ents has eosinophilic airway in amma on. When considering di erent asthma phenotypes with a possibly di erent origin of the disease, one can wonder whether the clinical usefulness of biomarkers of eosinophilia would be comparable between the phenotypes. In chapter 4 we have shown that phenotypic characteris cs do not in uence the accuracy of biomarkers of sputum eosinophilia. This despite the possible di erent underlying molecular pathways leading to in ammatory mechanisms in dis nc ve asthma phenotypes.25 Clinical characteris cs like obesity or smoking might also be of in uence on the in ammatory pathway and pa ern in asthma pa ents. The classical ac va on of eosinophilic airway in amma on in
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