Diagnosis
Pulmonary Function Tests
If symptoms and a patient's history strongly suggest asthma, the doctor will usually perform tests called pulmonary function tests to confirm the diagnosis and determine the severity of the disease.
Using a spirometer, an instrument that measures the air taken into and exhaled from the lungs, the doctor will determine several values:
- Vital capacity (VC), the maximum volume of air that can be inhaled or exhaled.
- Peak expiratory flow rate (PEFR), commonly called the peak flow rate, the maximum flow rate that can be generated during a forced exhalation.
- Forced expiratory volume (FEV1), the maximum volume of air expired in 1 second.
If the airways are obstructed, these measurements will fall. Depending on the results, the doctor will take the following steps:
- If measurements fall, the doctor typically asks the patient to inhale a bronchodilator medication. This drug is used in asthma to open the air passages. The measurements are taken again. If the measurements are more normal, the drug has most likely cleared the airways, and a diagnosis of asthma is strongly suspected.
- If measurement results fail to show airway obstruction, but asthma is still suspected, the doctor may perform a challenge test. It involves administering a specific drug (histamine or methacholine) that usually increases airway resistance only when asthma is present.
Allergy Tests
The patient may receive skin or blood allergy tests, particularly if a specific allergen is suspected and available for testing. Allergy skin tests help diagnose for allergic asthma, although they are not recommended for people with year-round asthma.

Review Date: 05/03/2011
Reviewed By: Harvey Simon, MD, Associate Professor of Medicine, Harvard Medical
School; Physician, Massachusetts General Hospital. Also reviewed by
David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.
A.D.A.M., Inc. is accredited by URAC, also known as the American Accreditation HealthCare Commission (www.urac.org)

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