Skin prick allergy test

Many parents recognize the signs of allergies in their children, including itchy eyes, runny nose, sneezing, and sore throat. And while the cause of allergies is often clear, sometimes moms and dads are left scratching their heads. Thankfully doctors can conduct allergy testing to pinpoint triggers and manage a child's reactions.

To understand allergy testing, it helps to know what causes allergies in the first place. Your child's immune system produces antibodies to fight viruses, bacteria, and toxins. But sometimes their body reacts to a harmless everyday substance—like a bite of egg or dust particles in the air—like it's a dangerous invader. If their body rejects pollen, for example, it might send chemicals to swell the lining of their nose, causing congestion and sneezing. Or if it's something they've eaten, the gastrointestinal lining gets inflamed, possibly leading to diarrhea.

To diagnose allergies, your child's pediatrician may recommend you to an allergist who can conduct testing, says Sanjeev Jain, M.D., a board certified allergist and immunologist at Columbia Allergy. "Allergy testing can be useful as a first step towards creating a plan to treat or reduce exposure to known allergens." Here's everything you need to know about the types of allergy tests available today. 

Preparing for Allergy Testing

The allergist may decide on a skin test, which involves placing certain allergens on or underneath the skin. There are three main types: skin prick test, intradermal test, and patch test. Alternately, the allergist may study blood removed from the vein. "Skin tests tend to be slightly better than blood tests at showing what bothers your child the most and give you results right away," says Sakina Bajowala, M.D., an allergist in North Aurora, Illinois, and mom of two sons with seasonal allergies. Because both tests can have false-positive results, an allergy diagnosis is usually made only when a child has obvious symptoms as well.

It's important to note that a number of over-the-counter and prescription medications, such as antihistamines, can prevent accurate results from a skin tests. Before scheduling a test, always inform your doctor of all the medications your child is taking. They may need to stop using these medications for up to two weeks beforehand.

Talk to your kid about allergy testing so they know what to expect before the appointment. Also consider bringing a distraction—like toys or a coloring book—to keep kids occupied while you wait for the results.

Skin Prick Test for Allergies

When It's Used

A skin prick test, also called a scratch test or percutaneous test, is especially useful in pinpointing potential food and environmental allergies. "It can also help identify the severity of these allergies based on the size of the reaction," says Dr. Jain.  "Skin prick testing is a common method since it offers immediate test results and may be less traumatic than a blood draw for some children."

Skin Prick Testing Procedure

Your child's arm or upper back will be used as the test site. After cleaning it with alcohol, the doctor places a drop of a solution containing the allergen on the skin, and a series of scratches or needle pricks allows the solution to enter it. 

To ensure accurate results, the scratch test will include histamine and glycerin, which are used as controls to make sure your child's skin is reacting normally. Histamine normally causes a skin reaction in most people, but glycerin usually causes no reactions—so if your child's skin reacts to glycerin, it may indicate that the skin is too sensitive for a skin prick test to work.

After the allergens are placed, the patient will wait 15-20 minutes to see if a reaction occurs. "If an allergy is present, they may develop an itchy, red bump at the location of the prick site on their skin," says Dr. Jain. These bumps (also called wheals) resemble mosquito bites, and they'll be measured and recorded by the doctor. 

Side Effects

The skin prick test itself isn't painful, but the most common reactions are itchy, swollen bumps on the skin. These usually subside in a few hours and disappear in a few days. In rare cases, the test can result in an extreme reaction if your child has a severe allergy to one of the tested substances.

Intradermal Test for Allergies

When It's Used

If additional testing is needed, the allergist may recommend intradermal testing. It's useful for identifying potential environmental allergies, and it can also pinpoint some medication allergies, says Dr. Jain. It's commonly used for detecting sensitivities to insect venom and penicillin.

Intradermal Testing Procedure

"This test uses a small needle to inject potential allergens in a liquid form under the top layer of skin, usually on your upper arms or forearms. After the allergens are injected, the patient will wait for 20 minutes to see if a reaction occurs to the allergens applied under their skin," says Dr. Jain. Like with the skin prick test, an allergic reaction is characterized by an itchy red bump at the injection site.

Side Effects

Redness and itching usually accompany an allergic reaction. According to Dr. Jain, the itching will resolve in several hours, and it can be managed with an antihistamine or topical medication. 

Patch Test for Allergies

When It's Used

"Patch testing can be very helpful in determining the cause of skin rashes and reactions that occur when an allergen touches the skin," says Dr. Jain. It detects contact dermatitis that normally appears within nine to 96 hours after exposure to the substance. One example is the rash that develops from poison ivy, but it can also appear from metals, perfumes, dyes, chemicals, beauty products, and more. Dr. Jain adds that unlike a skin prick test or an intradermal test, patch testing requires multiple visits to the allergist. (Her practice, Columbia Allergy, calls for three visits).

Skin Patch Testing Procedure

Adhesive patches containing certain substances are applied directly to the patient's skin—usually on their back. "The next two visits are 48 hours and 72 hours after the application of the patches," says Dr. Jain. "The patch will be removed at the second visit and an initial reading will be conducted. We're looking to see if the patient developed any redness, irritation, swelling, or a rash where the allergen was in contact with their skin." The final patch test reading will be performed at the third visit, as well as a discussion of the results.

Side Effects

Positive test results are characterized by itchy skin. Also, "late positive reactions may occur seven to 21 days after application of the panels, so it's important to follow up with the provider if you experience any delayed reactions," says Dr. Jain.

Blood Test for Allergies

When It's Used

Skin prick tests, intradermal tests, and patch tests look for a physical reaction to an allergen. The other option—blood tests—involve testing the patient's blood in a lab. Doctors may use this test if a child is on medication that could interfere with skin test results or if they have certain skin conditions like eczema. Blood tests may also be used if a severe allergic reaction is expected.

Allergy Blood Test Procedure

Blood is usually taken from a vein in the arm. In the lab, the experts will look for antigen-specific antibodies (IgE). "If antigen-specific antibodies exist, it means that the patient's body has identified this substance as foreign and has created antibodies to protect the body from this specific substance. If an allergen has high numbers of IgE, this typically indicates a more severe allergy," says Dr. Jain.

Side Effects

Your child might experience minor pain or bleeding at the needle prick site.

Which Allergy Test is Best for My Child?

There's no minimum age for allergy testing (although it's rarely done in children under 6 months), and your provider will determine the best option for your kid. That said, small children usually get the blood test or skin prick test for suspected environmental or food allergies. "A skin prick test may be less traumatic, but it may be difficult to perform if a child is unable to keep the allergens in place for 20 minutes or if a rash or eczema is present on the child's back," says Dr. Jain. "Blood tests can be more efficient, but the needle insertion can be traumatic for a small child. Plus, if the child is unable to stay still, it can be difficult to perform the blood draw." Both tests are equally effective at predicting allergies, so have faith in whatever method your provider chooses.

It's important to note that allergy skin tests (skin prick tests, intradermal tests, and patch tests) all carry a risk of acute allergic reaction. "The most common adverse symptoms include itching, burning, redness, mild swelling, and irritation to the allergy test application site," says Dr. Jain. "Most of these mild allergic reactions resolve after the allergens are removed."

Although very rare, skin allergy tests also post a risk of anaphylaxis. This is why allergy tests are done at a doctor's office, where emergency equipment and medications are on hand to counteract potential breathing difficulties.

My Child Has an Allergy—Now What?

If your child is diagnosed with an allergy, your doctor will advise on how to avoid the trigger. Various medications are also available to manage symptoms. For example, some antihistamines block the immune system from releasing histamine into the blood, stopping allergic reactions before they start or slowing them down once they have begun. Steroids work to decrease the inflammation caused by the immune reaction; these can be in the form of nasal sprays, eyedrops, and pills or liquids taken orally. Allergy shots, the injection of tiny doses of an allergen, are helpful for some patients; they work by producing antibodies against the allergen, preventing severe allergic reactions in the future.

Children who have previously had an anaphylactic or serious allergic reaction should carry a dose of epinephrine that can be injected by the child or their parents in case of an allergic reaction. Epinephrine is a hormone that helps to open up the airways to improve breathing, improve blood pressure, and decrease the allergic reaction. Whenever this medication is used, the child should be taken to an emergency room immediately.


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