There are some key asthma tests your doctor will use in diagnosing asthma. Some asthma tests, such as lung (or pulmonary) function tests, measure lung function. Other asthma tests can help determine if you are allergic to specific foods, pollen, or other particles. Blood tests give a picture of your overall health; specific tests also measure levels of immunoglobulin E (IgE), a key antibody that’s released during an allergic reaction. While everyone makes IgE, people who have allergies make larger quantities of this protective protein.
All of these asthma tests help your doctor determine if asthma is indeed present and if there are other coexisting conditions with asthma, such as allergies, GERD, or sinusitis. Once a proper asthma diagnosis is made, specific asthma medications can be prescribed to help manage your asthma and prevent asthma attacks.
Lung Function Tests
Lung function tests are asthma tests that assess lung function. The two most common lung function tests used to diagnose asthma are spirometry and methacholine challenge tests.
Spirometry is a simple breathing test that measures how much and how fast you can blow air out of your lungs. It is often used to determine the amount of airway obstruction you have. The methacholine challenge test may be performed if your symptoms and screening spirometry do not clearly or convincingly establish a diagnosis of asthma. Your doctor will know which test is best for your situation.
While a chest X-ray is not an asthma test, it may be used to make sure nothing else is causing your asthma symptoms. An X-ray is an image of the body that is created by using low doses of radiation to see internally. X-rays can be used to diagnose a wide range of conditions, from bronchitis to a broken bone. Your doctor may perform an X-ray exam on you in order to see the structures inside your chest, including the heart, lungs, and bones. By viewing your lungs, your doctor can see if asthma is likely to be causing your symptoms.
Evaluation for Heartburn and GERD
Gastroesophageal reflux disease, commonly called GERD, is another condition that may worsen asthma. If your doctor suspects this problem, he or she may recommend specific tests to look for it.
For more detail, see WebMD's article on Heartburn and Asthma.
For more detail, see WebMD's article on Allergies and Asthma.
Evaluation of the Sinuses
The presence of nasal polyps or sinusitis may make asthma harder to treat and control. Sinusitis, also called sinus infection, is an inflammation or swelling of the sinuses due to infection. When the sinuses become blocked and filled with fluid, bacteria grow, causing infection and inflammation. Your doctor may order a special sinus X-ray, called a CT scan, to evaluate your sinuses if he suspects an infection. Once acute sinusitis is diagnosed, you will be treated with antibiotics for at least 10 to 12 days. Treating the sinusitis may help in preventing asthma symptoms.
For in-depth information, see WebMD's Sinusitis and Asthma.
Judging the Severity of Asthma
Based on these asthma tests and your symptoms, your doctor may determine that you have asthma. The next step is for the doctor to determine the severity of asthma as this will help decide asthma treatment. There are four types of asthma determined by your symptoms and specific results from lung function tests. They are:
- Mild intermittent asthma. Symptoms occur less than twice a week with rare exacerbation or asthma attacks and infrequent nighttime asthma symptoms.
- Mild persistent asthma. Symptoms occur more than twice a week but less than once a day, and asthma attacks affect activity. People with mild persistent asthma do have nighttime symptoms more than twice a month.
- Moderate persistent asthma. Symptoms occur daily, with nighttime symptoms that occur more than once a week. People with moderate persistent asthma tend to have asthma attacks that affect their activity that may last several days. In addition, they require daily use of their quick acting asthma medication to control symptoms.
- Severe persistent asthma. Continual symptoms occur both day and night, and there is limited activity and frequent asthma attacks.