Diagnosing Asthma

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Harvard Medical School
Chrome 2001
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Diagnosing Asthma
Reviewed by the Faculty of Harvard Medical School

Diagnosing Asthma

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Diagnosing Asthma
Diagnosing Asthma
If your health care professional thinks you have asthma, he or she will take your history and may have you undergo several diagnostic tests.
InteliHealth/Harvard Medical Content


Your History And Exam
The story you tell your health care professional is one of the most important clues he or she will use to figure out if you have asthma. Spare no detail.
If you sometimes have trouble breathing, describe how you feel when you struggle for breath, and try to remember what you were doing just before it happens. Do you wake up at night short of breath? Does a nagging cough wake you at night but rarely trouble you during the day? Did a cold or the flu make it extra difficult to breathe? Do you have any allergies to animals or to something in your environment? Have you recently moved? Do you have a new job? Think of any changes — especially in your environment — that may be the cause of your breathing problems.
While you are telling your health care professional about your symptoms, he or she will be watching you for clues, such as whether you have trouble talking because your breathing is difficult or whether it seems as if it takes you extra physical effort to breathe in and out.
Using a stethoscope, your health care professional will check your lungs as you breathe, listening for the classic wheeze of asthma (a harmonica-like whining noise) as you breathe out. If it takes you longer than average to exhale each breath, this is a clue for your doctor that suggests asthma. Your health care professional also will look and listen for other causes of your breathing problems, such as an infection or signs of heart disease. If it looks as though asthma might be the cause of your symptoms, he or she may ask you to blow into a peak flow meter. He or she may also estimate the amount of oxygen in your blood by placing a probe over your finger.


Diagnosis And Tests
If your health care professional thinks you have asthma, a common way to confirm that diagnosis is to start an asthma treatment and see if you feel better. This means using an inhaler or a nebulizer to breathe in a drug that can open the airways. You may do this in the medical office or you may be sent home with one of these devices (and instructions on how to use it) to see if your symptoms improve over the next few days or weeks.
If this doesn't nail down the diagnosis, you may need to undergo further testing with one of the following:
Pulmonary function test. This is a more complicated and thorough version of a peak flow meter. It involves breathing into a machine that can take many measurements. In addition to testing the strength of your breaths, the machine can tell how much air your lungs can hold and whether the lung tissue shows any signs of damage. If a pulmonary function test shows measurable improvement after your doctor has had you breathe in an airway-opening drug, then you probably have asthma.
Most people with asthma do not have any lung damage in the soft air sacs of the lung (alveoli), even people who have had dramatic attacks. This shows that asthma is more a problem of the air tubes and not the lung tissue, where oxygen and carbon dioxide are exchanged. Other types of breathing problems such as chronic obstructive pulmonary disease and emphysema, damage the lung tissue itself.
Methacholine challenge test. Another test that helps confirm a diagnosis of asthma is the methacholine challenge test. This is a special drug test done at the same time as a pulmonary function test.
Your health care professional will ask you to inhale a drug (methacholine) that constricts the airways in some people. If your airways constrict, your doctor will then give you an airway-opening drug. People sensitive to methacholine who then respond to an airway-opening drug are likely to have asthma.

Unfortunately, the test is not 100 percent accurate. You could have a positive test result and not have asthma, or you could have a negative test result and have asthma. Still, a reaction to methacholine makes asthma a likely diagnosis for you.

Chest X-ray. Finally, you might be asked to have a chest X-ray. Although the resulting picture of your lungs isn't that helpful in diagnosing asthma, it can reveal other causes of breathlessness, such as pneumonia or heart failure.




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Last updated July 28, 2008

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