Asthma

Diagnosis

Diagnosing asthma can be difficult because many diseases cause similar symptoms. After your Mayo Clinic doctor discusses your medical history with you and conducts a physical examination, you'll undergo tests to rule out other medical problems. These tests also can identify factors that can make your asthma more troublesome or resistant to treatment. Your doctor will then use specialized tests — a number of them developed at Mayo Clinic — to assess your asthma. You'll likely undergo one or more of these tests:

• Allergy tests. An allergy skin test determines if allergens are a factor in your asthma. When a skin test isn't suitable, a blood test can help diagnose allergies.
• Lung (pulmonary) function tests. A lung function test measures the narrowing of your bronchial tubes. Your doctor may repeat this test to verify that your treatment is working and to determine how much medication you need.
• Methacholine challenge. This test can help your doctor diagnose asthma if your initial lung function tests are normal. Methacholine is a known asthma trigger that causes mild constriction of the airways in people who have asthma.
• Imaging tests. A chest X-ray and high-resolution computerized tomography (CT) scan of the lungs and sinuses identify any structural abnormalities or diseases (such as infection) that can cause or aggravate breathing problems.
• Rhinoscopy (nasal endoscopy) and upper airway endoscopy. Your doctor uses a fiber-optic scope with a camera attached (endoscope) to show your passageways, sinuses and upper airway. Nasal and sinus disorders are common in people who have asthma and may aggravate it.
• Sputum eosinophils. This test looks for certain white blood cells (eosinophils) in your sputum (matter discharged during coughing). Eosinophils are present when symptoms develop and become visible when stained with a rose-colored dye (eosin).
• 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.
• Exhaled nitric oxide test. Nitric oxide is a chemical marker of asthma. In this test, you breathe into an analyzer four or five times in 10 minutes to allow measurement of your nitric oxide levels.

Read more about allergy skin tests, chest X-ray, CT scan and nitric oxide test at MayoClinic.com.