A diagnosis of asthma is based on your medical history, a physical exam, and lung function tests.

Lung function tests

Lung function tests can diagnose asthma, show how severe it is, and check for complications.

• Spirometry is the most common test to diagnose asthma. It measures how quickly you can move air in and out of the lungs and how much is moved.
• Testing of daytime changes in peak expiratory flow (PEF) is done over 1 to 2 weeks. This test is needed when you have symptoms off and on but have normal spirometry test results.
• An exercise or inhalation challenge may be used if the spirometry test results have been normal or near normal but asthma is still suspected. These tests measure how quickly you can breathe in and out after exercise or after using a medicine. An inhalation challenge also may be done using a specific irritant or allergen if your doctor suspects occupational asthma.

Tests for other diseases

Asthma can be hard to diagnose because the symptoms vary widely. And asthma-like symptoms can also be caused by other conditions, such as a viral lung infection or a vocal cord problem. So your doctor may want to do one or more extra tests.

• More lung function tests may be needed if your doctor suspects another lung disease, such as COPD.
• An electrocardiogram (EKG, ECG) might be done to rule out serious conditions with similar symptoms, such as chronic heart failure. This test measures the electrical signals that control the rhythm of your heartbeat.
• A bronchoscopy test can be done to examine the airways for problems such as tumors or foreign bodies. This test uses a long, thin, lighted tube to look at your airways.
• Biopsies of the airways can be done to look for changes that point to asthma.
• A chest X-ray may be used to look for signs of other lung diseases, such as fibrous tissue caused by chronic inflammation (pulmonary fibrosis).
• Blood tests, such as a complete blood count (CBC), may be done to look for signs of an infection or other condition.

Regular checkups

You need to monitor your condition and have regular checkups to keep asthma under control and to review and possibly update your asthma action plan. Checkups are recommended every 1 to 6 months, depending on how well your asthma is controlled.

During checkups, your doctor will ask about information you may have tracked in an asthma diary, such as:

• Whether your symptoms and peak expiratory flow have held steady, improved, or become worse. You may be asked to bring your peak expiratory flow meter to an appointment so your doctor can see how you use it.
• Asthma attacks during exercise or at night.

Based on the results, your asthma category may change, and your doctor may change the medicines you use or how much medicine you use.

Tests to identify triggers

If you have persistent asthma and take medicine every day, your doctor may ask about your exposure to substances (allergens) that cause an allergic reaction. For more information about testing for triggers, see the topic Allergic Rhinitis.

Allergy tests can include skin tests and a blood test. Skin tests are needed if you are interested in allergy shots (immunotherapy).