Categorizing Asthma Severity

Asthma severity is typically classified according to lung function, and spirometry is the most accessible and useful lung function test for diagnosis and management of asthma [25] [23032465]. Spirometry is also indicated when there are atypical asthma symptoms, such as oppression in the chest or cough during exercise or when exposed to smoke, cold air, dust or when laughing, which usually suggests airway hyperactivity [26] [22364671]. We found that the exacerbation’s predicted probability led by spirometry increased and became one of the main indexes of asthma exacerbation risk in the 12-21 year-old group, showing that spirometry is a very important and reliable index for asthma diagnosis. The older the subjects are, more essential spirometry seems to be during asthma diagnosis.

We found that the subjects with more risk factors usually had higher predicted probability of asthma exacerbation, suggesting there risk factors could interact with each other and cause the mechanism of asthma complicated. As it is reported, obesity is related with smoking exposure[16] [27514726] and early-onset wheezing [19] [30209194], and it disproportionately affects racial/ethnic minorities [18, 27] [28030376, 29155689]; besides, smoke exposing could increase the risk of airway symptoms, such as dry cough at night and wheezing during or after exercise [28] [30082449], which are usually the sign of airway hyperactivity. Excluding spirometry, the risk factors’ influence on asthma exacerbation might weaken, as the same risk’s combination predicted probabilities usually decreased in older subjects. The asthma risk score has limitations related to generalizability. Firstly, the race/ethnicity proportion in the study is not equal to the world’s race/ethnicity proportion, thus the study population cannot represent the world population; moreover, miscegenation sometimes is difficult to distinguish, which might influence the racial/ethnic risk score analysis. Secondly, some unavoidable factors restricted our study, for example, we could not collect enough height and weight data among 0-11 year-old subjects and just showed the BMI analysis in 12-21 year-old subjects.

Thirdly, although we normalized the risk scores in this study, it was difficult to analyze the potential interaction among these factors, such as the correlation between obesity and smoking exposure [16] [27514726]. Last but not the least, asthma might be affected by some other risk factors, such as antibiotics use [29][27159872], diet [30] [28353635] and respiratory tract infections [31] [30217468], which were difficult to be normalized and analyzed in this study. In conclusion, in each group, the more total score the subject had, the higher predicted probability the subject would develop asthma exacerbation. The exacerbation’s predicted probability led by race, allergy and obesity became attenuate in the older age group, hinting that these risk factors might play greater roles during earlier life stage and have weaken influence as subjects get older. Besides, the correlation among race, allergy and obesity might enhance the risk factors’ influence on asthma development. The exacerbation’s predicted probability led by spirometry increased in older group, showing spirometry is a very important and reliable index for asthma diagnosis. This asthma risk score might be a simple, easy-to-use tool that, in this analysis, was capable of predicting asthma exacerbation.

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