BACKGROUND: The diagnosis of asthma is based on several characteristics including symptoms and suitable tests of airway lability. However, it is neither clear to what degree various tests and symptoms identify the same subjects, nor how these characteristics are best combined to diagnose asthma. The interrelationships between physician-diagnosed asthma, asthma-like symptoms, and abnormal airway function, as defined by four commonly used tests, have therefore been assessed. METHODS: A population based sample of 495 Danish schoolchildren aged 12-15 years, comprising 292 randomly selected subjects and 203 subjects considered at risk of having or developing asthma, was examined. Symptoms and background information were recorded by questionnaire. The test panel consisted of baseline forced expiratory volume in one second (FEV1%), provocation with treadmill exercise (EXE) and with inhaled methacholine (PD15), and monitoring of peak expiratory flow (PEF) twice daily for two weeks. RESULTS: The sensitivity for diagnosed asthma was highest for PD15 followed by PEF monitoring, whereas specificity for asthma or asthma-like symptoms was marginally higher with the other two tests. Most symptomatic subjects with any positive test were identified by PD15 alone (75%) or in combination with PEF monitoring (89%). PEF variability was more susceptible to treatment with inhaled steroids than the PD15 index. Although inter-test agreement was weak (kappa < 0.40 for all pairs), significant associations were found between PD15 and EXE, PEF and EXE, and FEV1% and PD15. CONCLUSIONS: The agreement between the four tests was weak. In particular, PEF variability and methacholine responsiveness seem to identify different varieties of airway pathophysiology. The combined use of methacholine provocation testing and PEF monitoring may be helpful as an epidemiological screening tool for asthma.
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