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Diagnosis of Asthma by Michelle Badash, MS

Asthma can be difficult to diagnose because the symptoms are sometimes similar to other lung conditions. Initially, your doctor will ask about your symptoms and medical history. A physical exam will be done.

In addition, the following tests may be performed:

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 demonstrated on 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 medicine” (such as albuterol), the obstruction is termed reversible. At this point, asthma is typically diagnosed.

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 imminent asthma attack or a need to change your medicine.

Provocation Test

People with asthma will experience 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 administered and the tests are run again. The diagnosis of asthma is usually made if the PFTs indicate lung airway obstruction during a provocation tests.

Allergy Tests

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.

Peak Flow Meter

References:

Symptoms, diagnosis and treatment. American Lung Association website. Available at: http://www.lung.org/lung-disease/asthma/learning-more-about-asthma/symptoms-diagnosis-and-treatment.html. Accessed September 14, 2012.
Asthma in adults and adolescents. EBSCO DynaMed website. Available at: https://dynamed.ebscohost.com. Updated September 7, 2012. Accessed September 13, 2012.
Asthma exacerbation in adults and adolescents. EBSCO DynaMed website. Available at: https://dynamed.ebscohost.com. Updated August 27, 2012. Accessed September 13, 2012.
Braunwald E. Harrison's Principles of Internal Medicine. 15th ed. New York, NY: McGraw-Hill; 2001.
Chinoy B, Yee E, Bahna SL. Skin testing versus radioallergosorbent testing for indoor allergens. Clin Mol Allergy. 2005;3(1):4.
Fonseca J, Costa-Pereira A, Delgado L, et al. Pulmonary function electronic monitoring devices: a randomized agreement study. Chest. 2005;128(3):1258-1265.
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: http://www.nhlbi.nih.gov/guidelines/asthma/asthgdln.htm. Accessed September 13, 2012.

Last reviewed October 2012 by Brian Randall, MD

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