FOOD ALLERGY TESTING FOR KIDS: SKIN PRICK VS PATCH TEST

Medically Reviewed by Dr. Sony Sherpa (MBBS) - May 06, 2022

What Is A Food Allergy?

A food allergy occurs when your child has a bad reaction to certain food. The immune system incorrectly recognizes substances in the food as something dangerous and reacts to it. Even though they have the same signs and symptoms, food allergy is different from food intolerance, which does not involve the immune system.

The majority of the food allergies in children are caused by peanuts, fish, shellfish, tree nuts, soy, wheat, eggs, and milk, of which the first four cause the most severe reaction. Food allergies affect 5% of children under the age of five.

Your child’s immune system releases chemicals known as histamines when exposed to allergy-causing foods. Histamines then reach various parts of the body through the bloodstream to cause symptoms. (1)

What Does A Food Allergy Look Like?

Allergic reactions to food may be mild or severe.

It generally begins as a runny nose, tingling in the lips and tongue, or an itchy rash. Other symptoms include belly pain, diarrhea, vomiting, nausea, cough, wheezing, hoarse voice, or tightness in the throat.

In the most severe and potentially life-threatening form, known as anaphylaxis, symptoms begin abruptly. This can involve multiple body systems causing difficulty in breathing, a drop in the blood pressure, swollen lips, and may even cause your child to faint. (1)

How Are Food Allergies Diagnosed?

Sometimes it is easy to figure out that your kid has a food allergy. For instance, hives or belly pain after eating peanuts. Other times it may be a bit puzzling. Because most foods have more than one ingredient, it is difficult to figure out the cause of allergy.

It is important to diagnose the cause of food allergy as the only treatment is to avoid the food that causes the symptoms. Your child’s pediatrician will make the diagnosis based on a thorough medical history and physical examination. To make an exact diagnosis of the cause of food allergy, allergy testing is required.

How Is Food Allergy Testing Done?

Allergists, the doctors who specialize in treating allergies, may recommend allergy tests to determine the culprit behind your kid’s food allergy. When done properly, food allergy tests are reliable and can rule out or rule in food allergies. It is important to remember these are different from food intolerance testing.

Some commonly performed food sensitivity tests for kids are:

• Skin test
• Blood test
• Oral food challenge
• Elimination diet

Let’s see how each of these allergy tests for kids is performed. (2,3)

Skin Test

There are two important skin tests for allergy: skin prick test and skin patch test.

So, what is a skin prick test?

The skin prick test, also termed a scratch or puncture test, is a procedure that involves placing tiny bits of suspected food on the skin of your kid’s forearm. The doctor then pricks the skin through the food, allowing the allergens to enter the body.

If your kid is allergic to any food, tiny red raised bumps appear on the skin where the food was placed. Reaction to a skin test typically develops within 15 minutes. This test is generally well-tolerated but must be performed under the supervision of an allergist.

A skin patch test is the gold standard test for delayed allergic food reactions. Unlike a skin prick test, a patch test does not involve needle pricking. Instead, allergens applied to patches are placed on your child’s skin.

The patches are worn for 48 hours, during which you should not bathe your child. Patches are removed thereafter, and irritated skin indicates an allergy.

You may wonder, what allergies are tested in a patch test? Any food substance that is suspected of causing food allergy can be tested in a patch test. Dry food is mixed with saline and then introduced as patches into your child's skin.

Are allergy patch tests accurate? As with any kind of skin test, they are not 100% accurate. A patch test may return a false negative report, not triggering any reaction even if your child is allergic to the food. It may also show a positive result when an allergy is not present.

Blood Test

Blood tests measure IgE antibodies to specific food allergens.

The most commonly performed blood test is RAST (radioallergosorbent test). Healthcare providers will draw blood from your kid’s arm. It can take anywhere between a few days to a week to get the results of RAST. There is no risk of allergic reaction with a blood test.

Oral Food Challenge

During an oral food challenge test, your child will be given food substances that may trigger allergic reactions. Your child will be asked to eat the food slowly in increasing amounts.

The test takes place in a doctor’s office, where your child will be closely monitored for symptoms of allergy. Your child’s doctor will be equipped with emergency medications during the entire procedure.

Elimination Diet

In a food elimination diet, the food that is thought to have caused allergy in your child will be eliminated from their diet. This is generally done for 2 to 6 weeks, after which the food is again re-introduced to them.

If the symptoms of allergy subside when the food is withdrawn and reappears upon reintroduction, this means your child is likely to have an allergy to it. These tests, however, cannot tell the difference between a food allergy and food intolerance.

How Long Does Allergy Testing Take?

The time taken for allergy tests depends upon the test being done.

A skin prick test takes around 20 to 40 minutes, including 15 minutes for the reaction to develop. The results of the skin patch test take 48 hours.

Blood test results may take several days or weeks. A food challenge test may take an entire day but typically takes 3 to 4 hours. The elimination diet test takes 2 to 6 weeks to complete.

The Takeaway

Food allergy tests are procedures the doctor uses to determine the cause of your child’s food allergy. They include skin tests like prick and patch tests, blood tests, challenge tests, and an elimination diet. These tests are simple, reliable, and always performed under the supervision of a doctor. If you suspect your child to have any type of food allergy, consult with a healthcare provider to get them tested.

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References

• Seth, Divya et al. “Food Allergy: A Review.” Pediatric annals vol. 49,1 (2020): e50-e58. doi:10.3928/19382359-20191206-01
• Muthupalaniappen, Leelavathi, and Adawiyah Jamil. “Prick, patch, or blood test? A simple guide to allergy testing.” Malaysian family physician : the official journal of the Academy of Family Physicians of Malaysia vol. 16,2 19-26.31 May. 2021, doi:10.51866/rv1141
• Spergel, Jonathan M, and Terri Brown-Whitehorn. “The use of patch testing in the diagnosis of food allergy.” Current allergy and asthma reports vol. 5,1 (2005): 86-90 doi:10.1007/s11882-005-0061-5

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