Bronchial hyperresponsiveness (BHR) is a key pathophysiological feature of asthma. Methacholine challenge test (MCT) is a common bronchoprovocation test useful for confirming a diagnosis of asthma. Studies of BHR in the general population of Asian countries are rare.

To estimate prevalence and determinants of BHR in Hanoi, Vietnam, and to study the association between BHR and symptoms common in asthma and previously diagnosed asthma.

1500 out of 5872 randomly selected adults in urban and rural Hanoi, who had participated in a questionnaire survey (83% participated), were randomly selected and invited to clinical examinations. Totally 684 subjects (46%) participated. MCT was performed in 366 subjects. BHR was defined as a FEV₁-decrease of ≥20% from baseline following methacholine inhalations (PC₂₀). Cut offs used in the analyses were PC₂₀ ≤ 1 mg/ml, ≤2 mg/ml and ≤8 mg/ml.

The prevalence of BHR was 16.4% at doses ≤8 mg/ml, while 9.6% reacted on doses ≤2 mg/ml. PC₂₀ ≤ 2 mg/ml was associated with FEV₁ <80% of predicted. PC₂₀ ≤ 2 mg/ml, but not PC₂₀ ≤ 8 mg/ml, was associated with multi-sensitization to airborne allergens. BHR defined as PC₂₀ ≤ 8 mg/ml was associated with age >45y. The combination of asthmatic wheeze (wheezing with breathlessness apart from colds) and BHR, irrespectively of magnitude of BHR, was more common than the combination of BHR with previously diagnosed asthma.

The results indicate BHR to be more common in Hanoi than previously found in south-east Asia. Although the prevalence of physician diagnosed asthma has increased in Vietnam, our results indicate that asthma still may be underdiagnosed in Vietnam.