Testing for Allergies
Lung Function Test
The lung (pulmonary) function test detects and measures airway obstruction and response to treatment, and is often repeated on a regular basis. The lung function test will help you and your Dakota Allergy & Asthma allergist determine how severe your asthma is and how much medication you need. Furthermore, the test will help assess if your current therapy program is effective. Pulmonary function tests (also called spirometry) are among the most important tests for asthma.
Some people with asthma have normal pulmonary function most of the time but have “twitchy” airways that react excessively to irritants. Your Dakota Allergy & Asthma allergist may order a test called a Methacholine challenge. For this test, you will be asked to breathe in a medication and the effect on your lungs will be measured to see if you react like someone with asthma. The effect of the medication is brief and can be reversed if needed with bronchodilator medicines.
Chest x-rays usually do not help in the diagnosis or treatment of asthma. If you have asthma, however, we may recommend a chest x-ray to determine if you have other conditions that mimic asthma.
Peak Flow Meter
Peak flow is the maximum speed that you can blow air out of your lungs after taking a full breath. You can measure your peak flow with a peak flow meter which is a device that measures changes in the size of your airways in liters per minute (peak flow rate).
In certain patients, regularly recording peak flow rates and keeping a diary of symptoms can help identify what triggers their asthma, give an early warning of an upcoming attack, and let them prevent worsening of their asthma by starting their action plan.
The Skin Tests
An allergy skin test may help diagnose the cause of the allergy. Skin tests are done on the arms or back using either the prick or intradermal method.
In the prick technique, a drop of an allergy-producing substance (allergen) is applied to the skin. The skin is then scratched or pricked. In the intradermal method, a tiny amount of allergen is injected into the skin. Skin tests for most allergens are safe, and the results are available in 20 to 30 minutes. Antihistamine and antidepressant medications affect skin tests and must be stopped before tests are begun. Some antihistamines can interfere with allergy skin tests for weeks. Check with your physician about stopping medications.
Skin tests for tobacco smoke allergy are not useful because tobacco smoke is an irritant, not an allergen.
Blood Allergy Tests
Allergies can also be diagnosed using a blood test. Examples include the radioallergosorbent test (RAST) or the ImmunoCap. They give information similar to the skin test. However, they are more expensive, may miss identifying some allergies, and also take longer to determine the results. The blood test can be used when a skin test would not be suitable. For example, it can be used when a person has a skin disease which does not allow skin tests to be done, or when taking an antihistamine or other medication that might affect skin test results.
Both skin and blood allergy test results must be interpreted by a physician who is experienced in diagnosing and treating allergies and who is familiar with your medical history.
Patient receives a prick allergy skin test