Asthma symptoms raise a red flag, but diagnosis requires evaluation and testing.
If you have bouts of wheezing, coughing and shortness of breath, your doctor may suspect asthma. But symptoms alone aren't enough to diagnose asthma. Your doctor will also ask about your symptoms and other health conditions. After gathering that information, your doctor may recommend a lung function (breathing) test or other tests. If your doctor suspects asthma, he or she may give you medication that reduces asthma symptoms. If the medication works, this suggests that you may have asthma. In some cases, other tests, such as lung function tests, are needed to confirm the diagnosis — and to make sure symptoms are not caused by something else.
Lung function tests
Although your symptoms, medical history and physical examination may suggest that you have asthma, lung (pulmonary) function tests may be needed to confirm an asthma diagnosis. Lung function tests may include one or more of the following tests.
Spirometry
This noninvasive test measures how well you breathe. During spirometry, you take deep breaths and forcefully exhale into a hose connected to a machine called a spirometer. Spirometry testing reveals two measurements that are important in diagnosing asthma:
- Forced vital capacity (FVC), which is the maximum amount of air you can inhale and exhale.
- Forced expiratory volume (FEV-1), which is the maximum amount of air you can exhale in one second.
Your doctor will compare these two measurements. If certain key measurements are below normal for a person your age, it may be a sign that your airways are obstructed. Your doctor may ask you to inhale a bronchodilator drug used in asthma treatment to open obstructed air passages and then try the test again. If your measurements improve significantly, it's likely that you have asthma. Your doctor may still suspect that you have asthma even if your initial spirometry measurements are normal. If so, you may need additional tests.
Challenge test
During this test, your doctor deliberately tries to trigger airway obstruction and asthma symptoms by having you inhale an airway-constricting substance or take several breaths of cold air. If you appear to have exercise-induced asthma, you may be asked to do vigorous physical activity to trigger symptoms.
After triggering your symptoms, you retake the spirometry test. If your spirometry measurements are still normal, it's likely that you don't have asthma. But if your measurements have fallen significantly, it may mean you have asthma.
Diagnosing asthma in children
When assessing children under age 5, doctors seldom conduct lung function tests because young children usually have trouble following the instructions. Instead, when a child's signs and symptoms, medical history and physical examination suggest asthma, the doctor may prescribe a bronchodilator — a drug that opens the airways. If your child's signs and symptoms improve after using the bronchodilator, an asthma diagnosis is likely.
Last Updated: 06/29/2007
