Asthma diagnosis and treatment
Spirometric criteria for asthma: Adding further evidence to the debate

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Background

Objective assessments of pulmonary function are considered essential for the diagnosis of asthma. The degree of reversibility of FEV1 considered supportive of asthma varies between international asthma guidelines.

Objective

We sought to compare the relative performance of international guideline reversibility criteria for identifying impairment in persons with a significant bronchodilator response (SBR) without an asthma diagnosis.

Methods

The North West Adelaide Health (Cohort) Study, a population biomedical study of 4060 subjects, conducted spirometry according to American Thoracic Society criteria. SBR was defined as postbronchodilator FEV1 responses of at least 12% or 15% of baseline values, 9% of predicted values, or 400 mL. A self-completed questionnaire assessed current asthma (CA), respiratory symptoms, and participant demographics.

Results

The prevalence of CA was 9.4% (n = 380), whereas 1.3% (≥400 mL) to 4.5% (≥9% of predicted value) of participants demonstrated an SBR in the absence of CA. With the exception of the 9% predicted criterion, prebronchodilator mean FEV1 (percent predicted) in those demonstrating an SBR but no CA was significantly worse than that in the CA group. Significantly more respiratory symptoms were experienced by the SBR groups than the group without asthma. Logistic regression analyses identified different characteristics of those classified by the following criteria: 12% and 15%, age of 40 years or greater and household income of less than $40,000; 9% predicted, household income of less than $40,000; 400 mL, male sex (odds ratio, 4.5; 95% CI, 2.1-9.3).

Conclusions

Different criteria identify different persons, but SBR by any criteria was associated with significant respiratory impairment, some of which might be attributable to asthma. Postbronchodilator change as a percentage of predicted value was the least biased of the criteria.

Section snippets

Methods

The methods of the North West Adelaide Health (Cohort) Study have been described previously.37 Briefly, all households in the northwest region of Adelaide that were listed in the electronic “White Pages” telephone directory were eligible for selection. A letter of introduction was sent to the household of each randomly selected telephone number. Selected households received a telephone call inviting the person with the most recent birthday and who was at least 18 years of age to participate in

Results

Complete spirometric and self-reported CA data were available for 4002 (98.5%) participants. Current asthma was reported by 9.4% (n = 380) of the study participants. Table I shows that the prevalence of reversibility in the population according to differing criteria ranged from 2.0% for the 400 mL or greater criterion to 6.2% for the 9% of predicted value or greater criterion. The prevalence of significant bronchodilator responsiveness (ie, reversibility without a CA diagnosis) ranged from 1.3%

Discussion

It is clear from this study that the 4 reversibility criteria classify quite different persons, which, although intuitive, has not been previously demonstrated in a large representative population sample. This has considerable implications for clinical practice and for the interpretation of epidemiologic studies examining asthma prevalence. Consistent with previous studies in COPD,25, 30 bronchodilator reversibility was normally distributed in the population. Consequently, there is likely to be

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    Supported by the University of Adelaide and the South Australian Department of Health.

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