How Is Asthma Diagnosed?

Methacholine Test

One of the tests used to help diagnose asthma is a methacholine challenge test. Methacholine is a drug that, when inhaled, causes an individual's airways to narrow slightly within the lungs, mimicking the effects of asthma on the lungs. This type of test can be performed in a pulmonary function lab or doctor's office. However, a methacholine test can be dangerous if individuals have low lung function, have had a stroke or heart attack within three months, have uncontrolled blood pressure, have suffered a brain or aortic aneurysm, or are pregnant or nursing. Before the test, patients will be asked to stop using inhalers or certain medications to make sure the result is accurate. The day the test is performed, patients shouldn't drink or eat any products containing caffeine. In addition, patients should talk to their doctor about any other factors that might affect the test, like exercise, upper respiratory infections, and smoking. The test begins with a spirometry test, and then increasing doses of methacholine are given through a nebulizer.

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