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Tests and diagnosis
By Mayo Clinic staffDiagnosing asthma can be difficult. Signs and symptoms can range from mild to severe and are often similar to those of other conditions, including emphysema, early congestive heart failure or vocal cord problems. In children, it can be hard to differentiate asthma from wheezy bronchitis, pneumonia or reactive airway disease.
In order to rule out other possible conditions, your doctor will do a physical exam and ask you questions about your signs and symptoms and about any other health problems. You may also be given lung (pulmonary) function tests to determine how much air moves in and out as you breathe.
Tests to measure lung function include:
- Spirometry. This test measures the narrowing of your bronchial tubes by checking how much air you can exhale after a deep breath, and how fast you can breathe out.
- Peak flow. A peak flow meter is a simple device that can be used at home to help detect subtle changes before you notice symptoms. If the readings are lower than usual, it's a sign your asthma may be about to flare up. Your doctor will give you instructions on how to track and deal with low readings.
Lung function tests often are done before and after taking a bronchodilator to open your airways. If your lung function improves with use of a bronchodilator, it's likely you have asthma.
Other diagnostic tests to diagnose asthma include:
- Methacholine bronchial challenge. If you have asthma, inhaling a known asthma trigger called methacholine will cause mild constriction of your airways. A positive methacholine test supports a diagnosis of asthma. This test may be used if your initial lung function test is normal.
- Nitric oxide test. This test is sometimes used to diagnose and monitor asthma. It measures the amount of a gas called nitric oxide you have in your breath. If your airways are inflamed — a sign of asthma — you may have higher than normal levels of nitric oxide. This test isn't widely available.
How asthma is classified
To classify your asthma severity, your doctor will evaluate your answers to questions about symptoms (such as how often you have asthma attacks and how bad they are), along with the results of your physical exam and diagnostic tests. Determining the severity level of your asthma will help your doctor choose the best treatment for you. Asthma severity often changes over time, requiring an adjustment to treatment.
Asthma is classified into four general categories:
| Asthma classification | Signs and symptoms |
|---|---|
| Mild intermittent | Mild symptoms up to two days a week and up to two nights a month |
| Mild persistent | Symptoms more than twice a week, but no more than once in a single day |
| Moderate persistent | Symptoms once a day and more than one night a week |
| Severe persistent | Symptoms throughout the day on most days and frequently at night |
