BACKGROUND: The diagnosis of asthma is not always straightforward and can be even more challenging in older adults. Asthma is ideally confirmed by demonstration of variable expiratory airflow limitation. However, many patients with asthma do not demonstrate airflow obstruction nor show bronchodilator reversibility. We aimed to investigate predictors for a positive bronchial challenge test with methacholine in older adults being evaluated for asthma. METHODS: This is a diagnostic accuracy study with a cross-sectional design. Participants ≥ 60 years with suspected asthma and a negative postbronchodilator response on spirometry were included. All participants underwent a methacholine challenge test (MCT). We assessed the value of standard asthma screening questions and additional clinical questions to predict the MCT results. A multivariable logistic regression model was developed to assess the variables independently impacting the odds of a positive MCT result. RESULTS: Our study included 71 participants. The majority were female (n=52, 73.2%) and the average age was 67.0 years. Those with a positive MCT (n=55, 77.5%) were more likely to have wheezing or coughing due to allergens (n=51, 92.7% vs. n=12, 75.0%; P=0.004) and difficulty walking several blocks (n=14, 25.5% vs. n=1, 6.3%, P=0.009). After adjustment, having wheezing or coughing due to allergens (OR=4.2, 95% CI 1.7–7.8, P=0.012) remained the only significant independent predictor of a positive MCT. CONCLUSIONS: In older adults with suspected asthma, questioning about wheezing or coughing due to allergens provides a modest independent value to predict a MCT result in those who previously had a negative postbronchodilator response on spirometry.