An allergy test is an exam performed by a trained allergy specialist to determine if your body has an allergic reaction to a known substance. The exam can be in the form of a blood test, a skin test, or an elimination diet.
Allergies occur when your immune system—your body’s natural defense— overreacts to something in your environment. For example, pollen, which is normally harmless, can cause your body to overreact. The body’s overreaction to the substance can lead to symptoms such as runny nose, sneezing, blocked sinuses, and watery eyes.
Types of Allergens
There are three types of allergens (substances that can cause an allergic reaction):
- Inhaled: These allergens affect the body when they come in contact with the lungs or membranes of the nostrils. Pollen is the most common inhaled allergen.
- Ingested: These allergens are present in certain foods such as peanuts, soy, and gluten.
- Contact: These allergens must come in contact with your skin to produce a reaction, such as the rash and itching caused by poison ivy.
Allergy tests involve exposing a person to a very small amount of a particular allergen and recording the reaction.
Why Allergy Testing Is Performed
Allergies affect more than 50 million people every year, according to the American College of Allergy, Asthma, and Immunology (ACAAI). Inhaled allergens are by far the most common type. Seasonal allergies and hay fever—an allergic response to pollen—affect more than 40 million Americans.
The World Allergy Organization estimates that allergies are responsible for 250,000 deaths annually (WAO).
Allergy testing is done to determine what particular pollens, molds, or other allergens a person is allergic to. You may need medication to treat your allergies. Or, you may want to simply attempt to avoid your allergy triggers.
How to Prepare for Allergy Testing
Before your allergy test, your doctor will ask you about your lifestyle, family history, and more.
You will most likely be told to stop taking the following medications prior to your allergy test, because they can affect the test results:
- antihistamines (both prescription and over-the-counter brands)
- certain heartburn medications
- omalizumab (Xolair) (an asthma medication)
- tricyclic antidepressants
How Allergy Testing Is Performed
An allergy test may involve either a skin test or a blood test. In the case of suspected food allergies, you may be put on an elimination diet.
Skin tests are used to identify numerous potential allergens. This includes airborne, food-related, and contact allergens.
Your doctor will typically try a scratch test first. During this test, an allergen is placed on a section of your skin. A technician uses a special tool to scratch the skin’s surface. You will be closely monitored to see how your skin reacts to the foreign substance. If there is no swelling or redness on the skin, you are not allergic to that specific allergen.
If the scratch test is inconclusive, your doctor may order an intradermal skin test. This involves injecting a tiny amount of allergen into your skin. Again, your doctor will monitor your reaction.
Another form of allergy skin test is the patch test. This involves using adhesive patches treated with suspected allergens. The patches will remain on your body after you leave your doctor’s office. The patches are then reviewed at 24 hours after application and again at 48 hours, if necessary.
In the case of severe allergic reactions, your doctor may determine that a skin test won’t work. Therefore, he or she may choose to have a sample of your blood drawn. The blood is then tested in a laboratory for the presence of antibodies that fight specific allergens. This test, called ImmunoCAP, is very successful in detecting antibodies to major allergens.
An elimination diet can help your doctor determine which foods are causing you to have an allergic reaction. It entails individually removing foods from your diet and later adding them back in. Your reactions will help determine which foods cause you problems.
The Risks of Allergy Testing
Allergy tests may result in mild itching, redness, or swelling of the skin. Sometimes, small bumps called wheals appear on the skin. These symptoms often clear up within hours, but may last for a few days. Mild cortisone creams can alleviate these symptoms.
On rare occasions, allergy tests produce an immediate allergic reaction that requires medical attention. In anticipation of such a reaction, allergy tests should be conducted in an office equipped with adequate medications and equipment. This includes epinephrine to treat anaphylaxis (a life-threatening allergic reaction).
If you develop a severe reaction after you leave the doctor’s office, call your doctor right away. If you experience symptoms of anaphylaxis—such as swelling of the throat, difficulty breathing, or low blood pressure—call 911 immediately, because this is a medical emergency.
After Allergy Testing
Once your doctor has determined which allergens are causing your symptoms, he or she will instruct you about how to avoid those allergens. Your doctor can also suggest medications that may ease your symptoms.