Diagnostic Tests in the Treatment of Asthma

What You Need to Know About Asthma Tests

During the process of being diagnosed with asthma or during the course of your treatment, you are likely to undergo different types of asthma tests. Some of the tests you may undergo fairly frequently, while you may never undergo others. Some you can do at home, while others may require you to go to your asthma provider's office, or you may even need to be referred to a more specialized physician.

Tests are only part of making an asthma diagnosis. Your doctor will not only ask about your asthma symptoms (wheezing, chest tightness, shortness of breath, and cough) but also about your family history, personal history  and perform a physical exam. Symptoms such as decreased exercise capacity or a night time cough are common among asthmatics. Likewise, symptoms are more likely to be asthma if they occur after exposure to furry pets, after exposure to high pollen levels, or exposure to dusts and molds. A personal history of atopic dermatitis, hay fever, and allergic rhinitis all increase your risk of asthma. Similarly, having a parent, brother or sister with asthma increases one's risk of developing asthma.

Peak Flow

Photo © A.D.A.M.

Peak Flow is probably the simplest test that you can use to see how well your asthma is doing and will be an integral part of your asthma care plan. Peak flows can easily be done at home with an inexpensive device called a peak flow meter. Peak flow measures how quickly air can be blown out of your lungs.

It is important for you to learn how to use your peak-flow-meter appropriately.

Peak flow is used to monitor rather than diagnose asthma. Normals are based on your age and height. It is important to determine your personal best peak flow so that you can base treatment changes off your asthma action plan.

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Asthma and Spirometry. Photo © A.D.A.M.

Spirometry is slightly more complicated than peak flow in that it is usually done in your doctor's office and measures both how much and how quickly air moves out of your lungs. This test is a better measure of your asthma severity over time. It is important in both the diagnosis and management of asthma over time.

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Complete Pulmonary Function Testing

Photo © Wikipedia user Steven Fruitsmaak

Your asthma care provider may want to determine your lung volumes and diffusing capacity. This is often done if your asthma diagnosis is unclear. The test requires you to sit inside a special box that helps determine how much air you breathe in and out.

  • Lung Volumes: Your asthma care provider may order body plethysmography test to determine your lung volumes. Asthma may cause certain changes in lung volumes that will assist your asthma care provider in diagnosing or treating your asthma.
  • Diffusion Capacity: Diffusion capacity measures how well oxygen flows from the lungs into your blood. Poor diffusion indicates damage to the lung where the oxygen and blood meet in the lungs. Diffusion capacity is usually normal in asthmatics.

Chest X-Ray

Asthma Chest X-Ray. Photo: Photodisc/ Getty Images

A chest x-ray is a test commonly performed for patients who wheeze. An asthma care provider will usually order one to make sure there is not some other condition that may be causing your symptoms like a lung infection. With asthma, the chest x-ray is likely to show air trapping or hyper-expansion.

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Bronchoprovocation Challenge Testing

Methacholine- Bronchoprovocation Challenge Testing. Photo © Flickr user Laurie Blundell

When your asthma provider orders a bronchoprovocation test, you will inhale a specific substance through a nebulizer, often methacholine or histamine. This is done to see if your lungs become irritated, hyperresponsive, and lead to the development of asthma symptoms. The test has a high negative predictive value. This means that if the test is negative it is unlikely you have asthma. It is often done when your asthma provider suspects asthma but is not able to make a clear diagnosis. Unlike looking for improvement in lung function, the bronchoprovocation test, is attempting to provoke asthma symptoms to make a diagnosis.

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Pulse Oximetry

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Pulse oximetry is a non-invasive way to measure oxygenation of blood or how well oxygen is being exchanged between the lungs and the blood. A sensor is placed on the fingertip or other thin part of the body with blood vessels close to the skin. The sensor measures changes in wavelengths of light and is able to estimate oxygenation in the blood. While some asthma patients like to have these devices at home, they are not usually part of an asthma action plan. They help a health care provider determine if you need oxygen acutely.

Arterial Blood Gas (ABG)

Photo © A.D.A.M.

An arterial blood gas (ABG) is an arterial blood sample used to determine how well blood is oxygenated -- a marker for oxygen exchange between the lungs and the blood. Commonly, a blood sample will be obtained from one of the arteries near your wrist. This test may likely be performed during an acute asthma exacerbation and is more reliable than pulse oximetry.

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Allergy Testing

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The relationship between allergies and asthma has been known for a long time. Allergens you normally breathe in can increase the inflammatory reaction and hyperresponsiveness in your lungs. However, your doctor cannot reliably determine if a particular allergen is responsible for your symptoms on clinical grounds alone. Because of this, your asthma care provider may recommend allergy testing. Not all asthmatics are tested. But if you have persistent asthma, your asthma care provider will probably recommend testing.


National Heart, Lung, and Blood Institute. Expert Panel Report 3 (EPR3): Guidelines for the Diagnosis and Management of Asthma

Clinical Pulmonary Function Testing, Exercise Testing, and Disability Evaluation, & Testing, Exercise Testing, and Disability Evaluation. In Chest Medicine: Essentials Of Pulmonary And Critical Care Medicine. Editors: Ronald B. George, Richard W. Light, Richard A. Matthay, Michael A. Matthay. May 2005, 5th edition.

Asthma. In Chest Medicine: Essentials Of Pulmonary And Critical Care Medicine. Editors: Ronald B. George et. al. May 2005, 5th edition.

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