Tehran University Medical Journal

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Background: Because bronchial hyper responsiveness (BHR) has been shown to be a risk factor for asthma and lung function decline, interest has focused on diagnosing BHR. The aim of our study was to measure the association between airway caliber relative to lung size expressed as the ratio between forced expiratory flow, mid expiratory phase, divided by forced vital capacity (FEF25-75/FVC) and BHR measured by methacholine challenge test (MCT) to obtain a cutoff for this ratio and positive MCT.
Methods: We carried out a cross- sectional study on general Iranian population in 376 subjects aged 7-73 years who were referred to Shariati hospital in Tehran, Iran in an outpatient setting. There were 190 male (50.5%) and 186 female (49.5%) subjects. They had chronic respiratory symptoms such as cough and dyspnea. The physical examination was normal. Baseline spirometry was normal or equivocal. MCT was done for all subjects over a two year period (2009- 2010). Positive MCT was defined by PC 20≤4mg/ml.
Results: The methacholine challenge test was positive in 191 (50.8%) and negative in 185 (49.2%) patients. The mean of FEF25-75/FVC in positive MCT was 0.86±0.27 Vs. 0.91±0.28 in the negative ones (p=0.070). The sensitivity and specificity of FEF25-75/FVC for prediction of MCT results were 57.1% and 60.2% based on cutoff point of 0.85 in all patients, and 87.5% and 70.7% based on cut off point of 1 in allergic patients, respectively.
Conclusion: The FEF25-75/FVC appears to be a useful predictive ratio in allergic patients but not in general population.

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Background: Asthma is a life-threatening disease that can cause death due to bronchospasm. In addition to clinical symptoms such as wheezing, acute paroxysmal dyspnea, chronic cough after exposure to cold air or cough after exercise, spirometry is also necessary for the diagnosis of asthma. The association between respiratory symptoms and a positive methacholine challenge test (MCT) is still controversial. The aim of this study was to determine the association between methacholine test results and respiratory symptoms and allergy.

Methods: One hundred and forty-six patients with respiratory symptoms and normal baseline pulmonary function tests were enrolled in this cross-sectional study. The participants were divided into two groups according to their positive or negative response to MCT. The association between MCT and the clinical symptoms and allergy was later evaluated statistically.

Results: Out of 146 participants of the study 59 (40.4%) were female and 87 (59.6%) were male. The mean age of the participants was 33.8±13.8 years. Sixty-one patients (41.8%) had positive results for the test. There was an association between a history of allergy, wheezing and age with positive MCT results. The other clinical signs had no association with the test.

Conclusion: Methacholine challenge test is the best diagnostic test for ruling out asthma in patients with normal pulmonary function tests in whom we cannot definitely rule out asthma based solely on clinical symptoms. Nevertheless, in adults with a history of allergy, wheezing and also in patients below 30, the probability for a positive MCT is high.