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Asthma is a chronic lung condition that causes trouble breathing. There is currently no cure for asthma, but treatment can help you manage your symptoms.

The first step to getting effective treatment is getting a diagnosis. There are several tests that might be used to diagnose asthma, including:

  • physical exams
  • lung function tests
  • imaging tests
  • blood tests

You might contact a doctor about asthma if you’ve been wheezing, coughing, and experiencing shortness of breath. Your doctor will go over your symptoms, medical history, and family history.

You’ll talk about how long you’ve had trouble breathing, how often it occurs, and if it gets worse at night. Your doctor will order tests to look for asthma and rule out other conditions that could be causing similar symptoms.

There are a number of tests needed to diagnose asthma. The first test you’ll have will be a physical exam. During the physical exam your doctor will:

  • examine your nose, throat, and airways
  • listen to your breathing with a stethoscope for wheezing sounds
  • examine your skin for eczema, hives, and other signs of a possible allergic reaction
  • discuss your symptoms

You’ll also have tests of your lung function, imaging tests, and blood tests. The results of these tests will be used to diagnose asthma or any other condition that might be causing your breathing symptoms. You can begin treatment once you have a diagnosis.

Lung function tests

Lung function tests are sometimes called pulmonary function tests. These tests are used to diagnose multiple lung and breath conditions, including asthma.

There are several common lung function tests you might have for asthma:

  • Spirometry. This test measures how much air you’re able to blow out of your lungs and how quickly you exhale the air. It allows doctors to see if your breathing is obstructed. You will have a spirometry test before and after inhaling a medication. The medication temporarily dilates your airways to assess the reversibility of obstructive lung disease.
  • Exhaled nitric oxide. Asthma is an inflammatory condition that impacts your lungs, and nitric oxide is a gas found in your lungs when they are inflamed. An exhaled nitric oxide test measures the nitric oxide in your lungs. You’ll breathe into a small machine for 10 seconds so that the amount of nitric oxide in your breath can be calculated. The amount of nitric oxide in a person’s exhaled breath can help diagnosis asthma, along with other tests. However, a normal level does not mean a person doesn’t have asthma.
  • Challenge tests. These tests are done if the results of your physical exam and spirometry aren’t clear enough for a diagnosis. Depending on what your doctor believes might trigger your asthma, you’ll either be given a substance such as mannitol or methacholine that can narrow your airways, or you’ll be asked to perform a brief exercise. You’ll then retake the spirometry test to see if your results change and get worse.
  • Peak expiratory flow measurement test. This test is normally given to people who already have an asthma diagnosis to measure how well their asthma management plan is working, but the test may be done during your initial testing as well. During this quick test, you’ll blow into a small meter to see how well air is moving in your lungs.

X-rays and other imaging tests

Your doctor might also order a chest X-ray or computerized tomography (CT) scan of the chest. These tests allow doctors to get a detailed image of your lungs and the surrounding structures. It can help your doctor look for other conditions that could be causing your symptoms, such as:

Tests for allergies, GERD, and other conditions

Multiple conditions can cause coughing and other symptoms that are similar to asthma. Sometimes, these conditions occur alongside asthma and can make your asthma worse. Your doctor will want to run tests for these conditions. The exact tests you’ll have will depend on your exact symptoms, and the results of your lung function tests. Possible additional tests include:

  • Gastroesophageal reflux (GERD) assessment. The diagnosis of GERD in people with asthma is often a clinical diagnosis, based on the presence of classic symptoms. For people with symptoms that are suspicious for GERD but who do not have the classic symptoms, the next step would be to refer them to a gastroenterologist for evaluation and workup.
  • Blood tests. There are no blood tests that can determine the presence or absence of asthma or gauge its severity. However, a complete blood count with differential white blood cell analysis to look for cells called eosinophils may be helpful in certain cases. Also, having a low amount of red blood cells (anemia) can cause shortness of breath that is unresponsive to asthma therapies and would require further evaluation to determine the cause. Certain blood tests can also look for allergies or infections that might be the cause of your symptoms.

Children under 5 years old don’t normally have lung function tests. Instead, a doctor will do a physical exam and make note of all their symptoms. They’ll collect a detailed medical history and will ask questions about the family medical history.

There are many conditions that might look like asthma in young children, making diagnosis difficult. Your child’s doctor might prescribe an inhaled medication called a bronchodilator. This medication is safe and temporarily opens the airways.

It might be a sign your child has asthma if the bronchodilator improves their breathing symptoms. Your child’s doctor will make a diagnosis once there is enough evidence to support that asthma is causing your child’s breathing difficulties.

Lung function tests are outpatient procedures. You’ll be able to drive yourself to your appointment and can return to your normal activities right away.

There are a few things to do before the day of the test. It’s best to talk with your doctor about any recent infections or immunizations you’ve had since those could impact your results. You can also ask them if there are any medications you need to stop taking before your test and when to stop taking them.

To prepare for general lung function tests, on the day of your testing, it’s important to avoid:

  • wearing tight-fitting clothes
  • coffee, soda, tea, and chocolate
  • exercise
  • cold air
  • eating a large meal less than 2 hours before your test

Your doctor will let you know if you need any additional testing, and what the preparation for those tests might be.

It often takes several tests before asthma is diagnosed. You might need:

  • a physical exam
  • multiple lung function exams
  • imaging tests
  • tests to rule out other conditions

The exact tests you’ll need to receive a diagnosis will depend on your symptoms and on the results of your initial lung function tests.

Children younger than 5 years old will have a physical exam, but they won’t have lung function tests. Doctors generally rely on symptoms and trials of bronchodilator medications to test for asthma in young children.