A diagnosis of asthma is based on your medical history, a physical exam, and lung function tests. If you developed asthma in adulthood, your doctor will ask about your job to determine whether you have occupational asthma.

Lung function tests can diagnose asthma, determine its severity, and check for complications.

• Spirometry is the most common test used to diagnose asthma. It measures how quickly you can move air in and out of your lungs and how much air is moved. The test helps your doctor decide whether airflow is decreased because of inflammation in the bronchial tubes and whether the tubes can return to their usual size in a short time after using medicine. Doctors also recommend the test at least every 1 to 2 years after asthma treatment has begun.
• 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.

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 whether your symptoms and peak expiratory flow have held steady, improved, or become worse and will ask about asthma attacks during exercise or at night. You track this information in an asthma diary. You may be asked to bring your peak expiratory flow meter to an appointment so your doctor can see how you use it. 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 for other diseases

Asthma sometimes is hard to diagnose because symptoms vary widely from person to person and within each person over time. Symptoms may be the same as those of other conditions, such as influenza or other viral respiratory infections or vocal cord dysfunction. Tests done to determine whether diseases other than asthma are causing your symptoms include the following:

• Additional lung function tests may be needed if other lung diseases, such as chronic obstructive pulmonary disease (COPD), are suspected.
• An electrocardiogram (EKG, ECG) measures the electrical signals that control the rhythm of your heartbeat. This test might be done to rule out serious conditions with similar symptoms, such as chronic heart failure.
• A bronchoscopy involves using a flexible scope called a bronchoscope to examine the airways. Occasionally airway problems such as tumors or foreign bodies will create symptoms that mimic those of asthma. The test might be done if you have unequal wheezing in the lungs or a poor response to asthma therapy. Biopsies of the airways can be done to look for changes characteristic of asthma.
• A chest X-ray may be used to see whether other lung diseases, such as fibrous tissue caused by chronic inflammation (pulmonary fibrosis), are causing symptoms.
• Blood tests may be done. For example, a complete blood count (CBC) may be done to look for signs of an infection or other condition.
• A sweat test, which measures the amount of salt in sweat, may be used to see whether cystic fibrosis is the cause of your symptoms.

Tests to identify triggers