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Diagnosis of Asthma
by Michelle Badash, MS
Asthma can sometimes be difficult to diagnose because the symptoms are sometimes similar to other lung conditions. Your doctor will ask about your symptoms and medical history. A physical exam will be done. The doctor will listen to your lungs.
Pulmonary Function Tests (PFTs)
Pulmonary function tests (PFTs) are done using an instrument known as a spirometer. The spirometer measures how much air is inhaled and expelled as you breathe. This test will measure both the amount and the rate of air that can pass through your airways.
The diagnosis of asthma is usually made when reversible lung airway obstruction is detected with PFTs. Lung obstruction means that the air passes too slowly through the airways. When the obstruction is corrected after you are given an inhaled dose of rescue medication, the obstruction is called reversible. At this point if the symptoms have been chronic, asthma is typically diagnosed. Your diagnosis may be reactive airway disease if the symptoms have been there for only a short time.
A peak flow meter measures the fastest rate at which you expel air. Peak flow meters can be used at home to assess if the degree of airway obstruction indicates an asthma attack will soon occur or that your medication may need to be changed.
Based on your history, physical, and pulmonary function tests the doctor will determine the severity of your asthma.
People with asthma will have a mild constriction of the airways when the drug methacholine is inhaled. If asthma is suspected, but there are no obvious symptoms of airflow obstruction on PFTs, methacholine is given and the tests are done again. The diagnosis of asthma is usually made if the PFTs indicate lung airway obstruction during a provocation test.
Allergy Tests TOP
You may have allergy tests if allergic asthma is suspected. A tiny allergen particle is placed under the skin with a needle. In the majority of cases, an allergic response is confirmed if the skin becomes raised or red within 20 minutes. Under some circumstances, the less accurate radioallergosorbent (RAST) test can be used to detect allergic responses.
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Asthma diagnosis. Asthma and Allergy Foundation of America website. Available at:
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Updated September 2015. Accessed September 8, 2017.
Diagnosing & treating asthma. American Lung Association website. Available at:
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Accessed September 8, 2017.
National Asthma Education and Prevention Program: Expert panel report III: Guidelines for the diagnosis and management of asthma. National Heart, Lung, and Blood Institute website. Available at: https://www.nhlbi.nih.gov/health-pro/guidelines/current/asthma-guidelines/full-report. Updated April 2012. Accessed September 8, 2017.
Last reviewed September 2017 by EBSCO Medical Review Board Michael Woods, MD, FAAP
Last Updated: 9/8/2017
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