Suitability of forced expiratory volume in 1 second/forced vital capacity vs percentage of predicted forced expiratory volume in 1 second for the classification of asthma severity in adolescents.
OBJECTIVE
To determine whether lung function alters asthma severity based on symptom history in asthmatic adolescents.


DESIGN
Data on asthma symptoms and lung function were collected from adolescents randomly selected from the general population.


SETTING
Five schools from the central Wellington, New Zealand, area during 2003 to 2005.


PARTICIPANTS
Two hundred twenty-four secondary school students aged 13 to 17 years (asthmatic, 118; nonasthmatic, 106).


MAIN EXPOSURES
Asthma questionnaire and lung function testing.


MAIN OUTCOME MEASURES
Distribution of asthmatic adolescents in each severity class based on symptoms, lung function, or a combination of both.


RESULTS
Median values for all spirometric parameters for asthmatic adolescents, apart from forced expiratory volume in the first second of expiration (FEV(1))/forced vital capacity (FVC), were in the normal range. Distribution of severity (based on symptoms and beta(2)-agonist use with adjustment for regular inhaled corticosteroid use) was 48.3%, mild; 28.8%, moderate; and 22.9%, severe asthma. For severity based on percentages of predicted FEV(1) and predicted forced expiratory flow, midexpiratory phase (FEF(25%-75%)) and FEV(1)/FVC, the percentages were 89.8%, 86.4%, and 63.5%, mild; 9.3%, 10.2%, and 18.6%, moderate; and 0.9%, 3.4%, and 17.8%, severe asthma, respectively. When percentages of predicted FEV(1) or predicted FEF(25%-75%) or FEV(1)/FVC were added to symptom severity, 6.8%, 5.1%, and 16.9% of asthmatic adolescents were reclassified into another severity group, respectively.


CONCLUSIONS
The majority of asthmatic adolescents have normal lung function despite experiencing significant asthma symptoms. Adding FEV(1)/FVC to symptom history changes the distribution of severity; however, both percentages of predicted FEV(1) and FEF(25%-75%) have little added effect in assessing asthma severity in adolescents.