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Health Conditions That Mimic Asthma

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How Are These Conditions Ruled Out and Asthma Correctly Diagnosed?

To make an asthma diagnosis and make sure your symptoms are not caused by another condition, your doctor will review your medical history, family history, and symptoms. He or she will be interested in any history of breathing problems you might have had, as well as a family history of asthma or other lung conditions, allergies, or a skin disease called eczema, which is related to allergies. It is important that you describe your symptoms in detail (coughing, wheezing, shortness of breath, chest tightness), including when and how often they occur.

You will be asked if you smoke now or have ever smoked. Smoking with asthma is a serious problem. Smoking is also a major factor in certain asthma mimics, including COPD and cancer. You will also be asked about past exposure to harmful chemicals, possibly at a job.

Your doctor will also perform a physical examination and listen to your heart and lungs.

There are many tests your doctor might perform, including lung function tests, allergy tests, blood tests, and chest and sinus X-rays. All of these tests can help your doctor determine if you have asthma and if there are other conditions affecting it.

For more information, see WebMD's article on Asthma Tests.

What Are Lung Function Tests?

Lung function tests (pulmonary function tests or PFTs) include several simple breathing tests to diagnose lung problems. The two most common are spirometry and methacholine challenge tests. These two tests, along with a history and physical exam, are the standards for making the diagnosis of asthma.

  •  Spirometry. This is a simple breathing test that measures how much and how fast you can blow air out of your lungs. Airway obstruction due to asthma or COPD is quickly revealed. Spirometry can be done before and after you inhale the asthma drugalbuterol, a bronchodilator. Albuterol delivered in an asthma inhaler helps open blocked airways. If the airway obstruction improves after albuterol, that indicates you have asthma or COPD. Your doctor can use other tests and your medical history to help determine which one you may have. This test might also be done at future doctor visits to monitor your progress and help your doctor determine if and how to adjust your treatment plan.
  • Flow volume loops. Simple spirometry tests only require that you exhale (blow out) forcefully, but flow-volume loops add rapid and maximal inhalation breathing maneuvers. Obstruction of air in the neck such as vocal cord paralysis or dysfunction are detected by this test. This upper airway narrowing can be confirmed using a CT scan of the neck or a flexible scope.
  • Methacholine challenge test (MCT). Even if lung function tests are normal, you can still have mild, intermittent asthma. Your doctor may order a methacholine challenge test. During this test, you inhale increasing amounts of a mist of methacholine before and after spirometry. If lung function drops by 20% or more after a low dose of methacholine, that indicates you have asthma. This small decrease does not cause a worrisome asthma attack, and the effects of the methacholine are always successfully treated with albuterol. 
  • Diffusing capacity (DLCO). This simple test includes a 10-second breath hold to determine how well the lungs take up oxygen from the lungs. The DLCO is normal in people with asthma and low in smokers who have COPD.

WebMD Medical Reference

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