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continued:

Asthma: Steps in testing and diagnosis

Physical exam

A physical exam for possible asthma generally includes:

  • An examination of your nose, throat and upper airways (upper respiratory tract).
  • Listening to the sounds your lungs make with a stethoscope as you breathe. Wheezing — high-pitched whistling sounds when you breathe out — is one of the main signs of asthma.
  • Examining your skin for signs of allergic conditions such as eczema and hives, which are often associated with asthma.

Lung function tests

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Image showing person using a spirometer Spirometer

Although your symptoms, medical history and physical examination may suggest that you have asthma, lung function tests (also called pulmonary function tests) may be needed to confirm an asthma diagnosis. Lung function tests may include one or more of the following tests.

Spirometry
This noninvasive test measures how well you breathe. During spirometry, you take deep breaths and forcefully exhale into a hose connected to a machine called a spirometer. Spirometry testing reveals two measurements that are important in diagnosing asthma:

  • Forced vital capacity (FVC), which is the maximum amount of air you can inhale and exhale
  • Forced expiratory volume (FEV-1), which is the maximum amount of air you can exhale in one second

Your doctor will compare these two measurements. If certain key measurements are below normal for a person your age, it may be a sign that your airways are obstructed. Your doctor may ask you to inhale a bronchodilator drug used in asthma treatment to open obstructed air passages and then try the test again. If your measurements improve significantly, it's likely that you have asthma. Your doctor may still suspect that you have asthma even if your initial spirometry measurements are normal. If so, you may need additional tests.

Exhaled nitric oxide test
A relatively new tool for measuring asthma, the nitric oxide test is available in only some hospitals and doctors' offices. High levels of nitric oxide gas in the air you breathe out can be a sign of asthma. Nitric oxide gas is produced by the body normally, but high levels in your breath can mean your airways are inflamed — a sign of asthma.

Challenge test
During this test, your doctor deliberately tries to trigger airway obstruction and asthma symptoms by having you inhale an airway-constricting substance such as methacholine. If you appear to have asthma triggered by exercise (exercise-induced asthma), you may be asked to do vigorous physical activity to trigger symptoms.

After triggering your symptoms, you retake the spirometry test. If your spirometry measurements are still normal, it's likely that you don't have asthma. But if your measurements have fallen significantly, it may mean you have asthma.

When checking children under age 5, doctors seldom conduct lung function tests because young children usually have trouble following the instructions. Instead, when a child's signs and symptoms, medical history, and physical examination suggest asthma, the doctor may prescribe a bronchodilator — a drug that opens the airways. If your child's signs and symptoms improve after using the bronchodilator, an asthma diagnosis is likely.

Additional tests: Ruling out conditions other than asthma

Depending on your age, your medical history and initial testing, your doctor may suspect that you have a condition other than asthma. Conditions that can cause asthma-like symptoms include:

  • Other lung disease such as chronic obstructive pulmonary disease (COPD)
  • Airway tumors
  • Airway obstruction
  • Bronchitis
  • Lung infection (pneumonia)
  • Blood clot in the lung (pulmonary embolism)
  • Congestive heart failure
  • Vocal cord dysfunction
  • Viral lower respiratory tract infection

If your doctor suspects that you have another condition, you may have other tests, such as:

  • Chest and sinus X-rays
  • Complete blood count
  • Computerized tomography (CT) scans of the lungs
  • Gastroesophageal reflux assessment
  • Sputum induction and examination

Your doctor may also want to see whether you have any other conditions that can accompany asthma. These include:

  • Heartburn, or gastroesophageal reflux disease (GERD)
  • Hay fever
  • Sinusitis

Your doctor may also perform allergy tests. Although allergy tests aren't used to diagnose asthma, they can help identify substances that may be causing or worsening your asthma.

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References
  1. Expert Panel Report 3 (EPR-3): Guidelines for the diagnosis and management of asthma — Summary report 2007. National Heart, Lung, and Blood Institute. http://www.nhlbi.nih.gov/guidelines/asthma/asthsumm.htm. Accessed June 5, 2009.
  2. Asthma in infants. Asthma and Allergy Foundation of America. www.aafa.org/print.cfm?id=8&sub=17&cont=160. Accessed June 5, 2009.
  3. Wheezing and asthma in infants. KidsHealth. www.kidshealth.org/PageManager.jsp?dn=KidsHealth&lic=1&ps=107&cat_id=20564&article_set=37965. Accessed June 5, 2009.
  4. Stewart L. Exhaled nitric oxide. Immunology and Allergy Clinics of North America. 2007;27:571.
  5. American Thoracic Society. ATS/ERS recommendations for standardized procedures for the online and offline measurement of exhaled lower respiratory nitric oxide and nasal nitric oxide, 2005. American Journal of Respiratory and Critical Care Medicine. 2005;171:912.

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June 24, 2009

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