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If symptoms and a patient's history strongly suggest asthma, the doctor will usually perform tests known as 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:
If the airways are obstructed, these measurements will fall. Depending on the results, the doctor will take the following steps:
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.

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