Diagnosis

Physical exam

Your doctor will perform a physical exam to rule out other possible conditions, such as a respiratory infection or chronic obstructive pulmonary disease (COPD). Your doctor will also ask you questions about your signs and symptoms and about any other health problems.

Tests to measure lung function

You may be given lung function tests to determine how much air moves in and out as you breathe. These tests may include:

• Spirometry. This test estimates 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 measures how hard you can breathe out. Lower than usual peak flow readings are a sign that your lungs may not be working as well and that your asthma may be getting worse. Your doctor will give you instructions on how to track and deal with low peak flow readings.

Lung function tests often are done before and after taking a medication to open your airways called a bronchodilator (brong-koh-DIE-lay-tur), such as albuterol. If your lung function improves with use of a bronchodilator, it's likely you have asthma.

Additional tests

Other tests to diagnose asthma include:

• Methacholine challenge. Methacholine is a known asthma trigger. When inhaled, it will cause your airways to narrow slightly. If you react to the methacholine, you likely have asthma. This test may be used even if your initial lung function test is normal.
• Imaging tests. A chest X-ray can help identify any structural abnormalities or diseases (such as infection) that can cause or aggravate breathing problems.
• Allergy testing. Allergy tests can be performed by a skin test or blood test. They tell you if you're allergic to pets, dust, mold or pollen. If allergy triggers are identified, your doctor may recommend allergy shots.
• Nitric oxide test. This test measures the amount of the gas nitric oxide in your breath. When your airways are inflamed — a sign of asthma — you may have higher than normal nitric oxide levels. This test isn't widely available.
• Sputum eosinophils. This test looks for certain white blood cells (eosinophils) in the mixture of saliva and mucus (sputum) you discharge during coughing. Eosinophils are present when symptoms develop and become visible when stained with a rose-colored dye.
• Provocative testing for exercise and cold-induced asthma. In these tests, your doctor measures your airway obstruction before and after you perform vigorous physical activity or take several breaths of cold air.

How asthma is classified

To classify your asthma severity, your doctor will consider how often you have signs and symptoms and how severe they are. Your doctor will also consider the results of your physical exam and diagnostic tests.

Determining your asthma severity helps your doctor choose the best treatment. Asthma severity often changes over time, requiring treatment adjustments.

Asthma is classified into four general categories: