9 Things You Need to Know About Food Allergy Testing
Food allergy testing, including things like a skin prick test, is one of the best ways to find out if you truly have a food allergy.
Food allergies are a serious problem and they have been on the rise in the last 20 years. They affect over 7 percent of the Canadian population. Many children outgrow food allergies, but others remain allergic well into adulthood. What’s more, some people even develop new food allergies as adults.
When you have a food allergy, your immune system reacts to the food as if it is a dangerous invader. It mounts an attack that leads to allergy symptoms such as hives, abdominal pain, and even anaphylactic shock, the most serious and potentially life threatening type of allergic reaction.
Undergoing food allergy testing is the safest and most efficient way to identify a potential food allergy. The most common food allergies are to milk, soy, wheat, eggs, tree nuts, fish, shellfish, and peanuts. Once the problematic food or foods are identified, the best way to prevent allergic reactions is to carefully avoid the food in the future.
This can be difficult, particularly for children and when eating in restaurants, as every ingredient needs to be scrutinized. However, it’s often the best way to stay safe.
Food allergy vs. food sensitivity
A food sensitivity, or food intolerance, is often confused with a food allergy. While the symptoms often overlap, the complications vary dramatically. A food sensitivity means that your body has trouble digesting a specific food. Symptoms are generally limited to digestive problems, including abdominal pain, nausea, gas, and diarrhea.
Common causes include lactose, an enzyme found in diary; monosodium glutamate (MSG), a flavour enhancer, FODMAPs, a type of carbohydrate found in certain foods; and gluten, which can cause a food sensitivity in some people and the serious autoimmune condition known as celiac disease in others.
A food allergy is an immune reaction that can impact various organs and can cause potentially dangerous symptoms. Symptoms can include some of the same digestive issues as food sensitivities, but the allergy also manifests in the skin, with symptoms such as hives, tingling, itching, and redness, and the respiratory system, with coughing, wheezing, nasal congestion, trouble breathing, and tightness in the chest.
While food sensitivities can be uncomfortable, food allergies can sometimes be potentially life threatening.
What are food allergy tests?
Food allergy tests are conducted to find out if you have an allergy or sensitivity to a particular food. “They are used to diagnose IgE-mediated food allergy, or the type of allergy that puts you at severe risk of reaction [anaphylaxis],” says Stephanie Leeds, MD, allergist and assistant professor at Yale School of Medicine in New Haven, Connecticut.
IgE stands for immunoglobulin E, a type of immune system antibody that triggers histamine in the body and allergy symptoms.
Skin test or skin prick test
Conducted by an allergist, this test involves placing a small amount of the suspected allergen on the skin, usually the forearm, and then pricking the area with a skin testing device. This allows the food protein to get beneath the skin. If there is an allergy to it, a red, itchy bump will appear.
This type of test is easy to perform and can be used to screen for allergies to several different types of food at once. Skin testing is generally not painful, and no blood is drawn. The devices “often do not have needles, they are almost like plastic forks/tines,” explains Dr. Leeds. Skin testing results are clear and often happen relatively quickly, within about 15 minutes.
As for side effects, patients may have small areas of redness and swelling after the skin testing is complete, “but this typically fades quickly without any intervention,” she says.
A blood test involves testing the blood for IgE antibodies. They can form after a person is exposed to a food, generally after eating it, although they can even be present at birth. “Some infants are born with food specific IgE levels detectable in the blood,” Dr. Leeds explains.
The presence of IgE antibodies to a specific food is known as sensitization, and it doesn’t mean you definitely have an allergy to that food or will have symptoms when you eat it. The presence of the antibodies just means the body recognizes the food as a possible allergen, and you might have symptoms.
However, if you are experiencing food allergy symptoms, these types of blood tests can help track down and confirm the source of the problem. It generally takes less than five minutes to draw the blood, but can take a few days or even weeks to get the test results.
“A blood test requires a venipuncture with a butterfly needle,” says Dr. Leeds. “All blood draws (for any blood test) are similar. They involve the prick of a needle as it goes into the vein to retrieve blood.”
Oral challenge test
An oral challenge test involves orally administering small amounts of the food in question to see how a person reacts. They aren’t done as frequently as other tests due to the risk of having a severe reaction. You’ll be closely monitored by your allergist to see if you have allergy symptoms. If you do, you will immediately be treated to prevent a severe reaction.
Dr. Leeds dubs the oral challenge the “gold standard” for diagnosis of food allergy, so they are used when clinical history and/or testing does not definitively support an allergy. For example, if someone has never ingested a food but other tests suggest there might be a problem, a physician may choose to perform an oral food challenge.
If someone had a questionable reaction on other tests, a physician may also choose to perform an oral food challenge. “You can do a food challenge to essentially any food,” she notes. There is no pain involved in the oral challenge method. “It is the simple act of ingesting a food over time,” she says.
If a patient tolerates a food during a challenge, they are usually cleared as not having a food allergy. “If they have a reaction during a challenge, we may need to treat them with medications including injectable epinephrine,” Dr. Leeds explains. (Epinephrine is the allergy-stopping medication found in EpiPens.)
Should you try an elimination diet?
The elimination method involves removing the suspected foods from your diet altogether. Then you’ll add the foods back into your diet, one at a time, looking for a reaction.
The elimination diet is not recommended for anyone at risk for a severe reaction, and it can’t determine whether a reaction is due to a food sensitivity or an allergy.
“As a food allergist, I never recommend food elimination as a way to diagnose food allergies. All too often, we have patients that have eliminated foods unnecessarily, and this period of avoidance actually puts them at risk of developing an allergy over time,” says Dr. Leeds.
“We know that food tolerance is promoted by consistent exposure through the gut (eating), and avoidance in certain individuals can lead to allergic sensitization,” she says.
Do food allergy tests really work?
The answer is yes. Food allergy testing is generally considered accurate. However, the accuracy can depend on a few factors.
They can help rule out a food allergy
Dr. Leeds explains that food allergy tests have excellent track record for ruling out food allergies, but positive results on the tests are harder to interpret. So, if the results are negative, the chances are good you are not allergic to that food. However, if the results are positive, it’s less clear when it comes to accurately diagnosing if you are indeed allergic to a specific food.
Positive results can range from low to high
A positive result on a skin or blood test isn’t a simple yes or no result—they can range from a weak to a strong reaction.The stronger the results or reaction—the bigger the skin reaction or the higher the level of IgE on a blood test—the better the chance that you are truly allergic to a food. “The larger the size of the skin test or the higher the level in the blood, the more likely they are true positive test results,” Dr. Leeds states.
They cannot determine allergy severity
While food allergy testing can help identify the food in question, it cannot determine just how allergic someone is to it. “The size or degree of testing does not correlate with severity of allergy,” says Dr. Leeds. So, allergy testing can’t really tell you if you’ll have hives and itchy lips when eating a food or if you’ll have dangerous reaction. And just because you haven’t had a serious reaction in the past, it doesn’t mean you can’t have one in the future when encountering a food.
The more experienced the tester, the more accurate the results
Testing should be done by a board-certified allergist who understands the nuances of testing and can create a clear pretest predictive calculation, suggests Dr. Leeds. “Anyone unfamiliar with allergy testing should not be ordering these diagnostic tests, and food allergy screening panels should almost never be ordered,” she states.
Oftentimes, multiple tests are needed, and a skilled physician is needed to interpret the results. Dr. Leeds reveals that no single test is entirely accurate. “An allergist often needs to triangulate the clinical history, skin test, and blood test to determine whether or not to offer a diagnostic oral challenge.
Should you try an at-home food allergy test?
Dr. Leeds notes that there are many commercially available blood and skin tests for many foods, with the main ones being milk, egg, wheat, peanut, tree nuts, fish, shellfish, soy, and sesame.
Some at-home tests look for IgE or a separate antibody, known as IgG, which they say can detect food sensitivities. (You generally put a drop of a blood on a card from a kit and send it in to be tested.)
However, these tests aren’t accurate for diagnosing food allergies, Dr. Leeds says. “Our skin and blood tests look for food specific IgE, not IgG,” explains Dr. Leeds. “IgG testing generally represents an exposure to a food, rather than allergy to a food, and has no bearing on food allergy diagnosis.”
She suggests avoiding commercially available “food intolerance” test kits, as they “are not validated for the diagnosis of food allergy, and are often expensive and clinically irrelevant.”
Who should get tested?
Anyone who has experienced what seems like an immediate allergic reaction after eating a food, and who is now strictly avoiding those foods, is a good candidate for food allergy testing. “Immediate reactions happen within minutes to two hours after exposure (generally speaking), and typical symptoms include hives, swelling, itching, coughing, wheezing, sneezing, vomiting, and passing out,” specifies Dr. Leeds.
Dr. Leeds notes that people should not get tested unless they have a very convincing history of an allergic reaction to a food and a physician recommends testing.
How to prepare for food allergy testing
In preparation of food allergy testing in the form of a skin test, patients should avoid taking any antihistamines for a week before testing. However, there is no specific preparation for a blood draw, per Dr. Leeds. She adds that there is no specific preparation for an oral food challenge either. “Patients need to come hungry, without fever or sick symptoms, and off of antihistamines,” she says.
Costs of food allergy testing
Whether or not food allergy testing will be covered by insurance depends on patients’ insurance companies and reimbursement rates, “but most patients are able to get tested without significant cost,” says Dr. Leeds. Also, costs will vary depending on the type of food allergy test you take.
Next, find out What Hypoallergenic Really Means