The behavior of allergies varies considerably from one individual to the next. There is no exact formula for predicting how skin prick reactions or antibody levels will translate to allergy symptoms. This can make diagnosing allergies complicated and leave much room for uncertainty in the interpretation of test results. For my last post in this series on food allergies, I will discuss identification and therapy options currently available along with their limitations.
Before I proceed, the obvious should be noted; I am not a doctor. Your diagnosis and treatment plan should be reviewed with your medical provider. The purpose of this post is simply to supply information on some of the routes available.
Can’t I just diagnose my own allergy?
Many people take it upon themselves to diagnose their own allergies. While this may work in cases where severe reactions can be linked easily to certain foods, it’s generally not a reliable method and can lead to unnecessary dietary restrictions. Even for practitioners with years of experience, establishing an allergy can be tricky.
Sensitization gets mentioned a lot with allergy tests. Is it the same thing as an allergy?
Sensitization is not synonymous with allergy. Sensitization means the body has created defensive proteins (antibodies) to a particular substance it has deemed a potential threat. Sensitization may be asymptomatic, but symptoms must be present with an allergy. All allergies require sensitization; not all sensitizations become allergies.
How is an allergy diagnosed?
Diagnosing an allergy is a multi-step process. First, the clinical history of the patient should be assessed including family background and range of symptoms. The second step is typically a skin prick test. Additionally, an IgE serum analysis may be performed. After all that, a double-blind, placebo-controlled food challenge test may be conducted. The food challenge test is the gold standard for allergy identification and is the only way to conclusively determine the presence of an allergy and its level of reactivity.
What exactly does a skin prick test measure?
The skin prick test is often one of the first tools utilized to diagnose a food allergy. It is used to ascertain IgE sensitization to certain foods. For this test, the skin is lightly punctured in the presence of an allergen. This puncturing is done to allow mast cells in the skin to associate with the allergen. If IgE antibodies are present and cause mast cells to degranulate, histamine will be released, and a welt will form. This signifies a possible sensitization.
Why isn’t a skin prick test enough?
Skin prick tests are very accurate (90%) in proving someone is not allergic to a food, but they are much less successful in proving they are allergic. False positives are so common only 50% of reactions actually coincide with an allergy. Therefore, a skin prick test is not enough to verify an allergy to a given food. However, a history of reacting to a food and a positive skin prick test together are much more conclusive than a skin prick test alone. It should be noted, skin prick tests are only relevant for hypersensitivity reactions mediated by IgE. Delayed reactions like those facilitated by T cells cannot be detected via this method. As one final caution, you should pay no heed to the size of the welts created during this test. Although it may seem logical, bigger welts do not correlate with worse allergies.
If skin prick tests are regularly inaccurate, why are they performed so often?
The skin prick test does have many drawbacks, but it generally takes less than 15 minutes and only causes marginal irritation to the patient. Hence, its popularity.
What about IgE serum tests?
IgE serum assessments like fluorescent enzyme immunoassay and radioallergosorbent tests ascertain the presence of IgE antibodies in the blood to specific allergens. These tests only require a blood draw, which makes them particularly appealing. Unfortunately, they also have sizeable disadvantages.
Skin prick and IgE serum tests share some downsides. Both only detect sensitization, and they don’t detect it that well. Like a positive skin prick test, even if you have IgE antibodies to a particular food, it does not automatically follow that the food will cause allergy symptoms. Further, quantities of IgE do not correlate with severity of reactions. You could have a large amount of IgE in your blood for a specific allergen and tolerate it, or you could have a slightly positive test result for a food that elicits horrible reactions.
If skin prick and serum tests aren’t enough, what then?
Only those patients that have had a severe systemic reaction after ingesting a food and have a positive skin prick test need no further confirmation of their allergy. For everyone else, verification requires a double-blind, placebo-controlled food challenge.
A double-blind, placebo-controlled food challenge (DBPCFC), also called an oral challenge test, is the best way to diagnose a food allergy. Due to the chance of a severe reaction, this test is usually done at a hospital under medical supervision. The challenge starts with the patient consuming an amount of the suspected food so miniscule it’s not likely to cause a reaction or an identical amount of a placebo. The dose taken is doubled again and again until a normal amount of the food is being consumed. If a reaction occurs, the test is halted as needed.
Why the placebo control for the oral challenge test?
Patients may have anxiety about the possibility of having a reaction. This concern may lead them to believe they are having a reaction when they are not. The placebo control rules out these anxiety-driven false outcomes.
What about patch testing?
Patch testing involves the application of suspected allergens to the skin for two days. Each allergen solution is contained in a disc that is held in place with hypoallergenic tape. Often, a large panel of substances is screened at the same time, which can uncomfortably take up all the space on someone’s back. I think my doctor packed about 90 compounds on mine. Patch testing is performed to ascertain delayed-type reactions, such as those mediated by T cells instead of IgE. These include nickel and fragrance allergies. And yes, you can react to those substances in your food. Patch testing can also be useful when investigating possible causes for eosinophilic esophagitis, an allergic condition that triggers inflammation in the esophagus.
How does a food diary fit in?
A food diary can be helpful when investigating dietary issues of any sort whether they be allergies or other adverse reactions. It can be particularly valuable in uncovering routines of reaction and obscure problem ingredients. In a food diary, everything consumed is recorded from drinks to cough drops.
What about unconventional means of allergy diagnosis?
Those that suffer from allergies or have children that do can be taken advantage of by purveyors of diagnostic methods that lack scientific credibility. These unproven procedures include hair analysis, IgG testing, electroacupuncture, and muscle testing. While it is possible that some of these analyses will have enough research behind them to validate their use at some point, that is not the case today. Don’t be exploited in your eagerness for answers.
Are there treatments for allergies beyond avoidance?
While avoidance is the only treatment for allergies that is completely successful, other approaches like immunotherapy have merit in many cases.
The goal of immunotherapy is to switch the body’s attitude to a food from allergy to tolerance. Immunotherapy involves eating daily doses of the allergen that slowly increase over time. This regular exposure in growing concentrations can lead to desensitization, which means reactions will be less acute and greater quantities of the allergen will be necessary to elicit them. Unfortunately, immunotherapy requires many doctor visits, often causes mild to moderate reactions throughout, and has the potential to cause severe reactions. Further, the most advantageous dosing amounts and periods are still being debated. Yet, this approach will likely become more common in the future since it has been shown to discontinue reactions in 50% of patients, which is called sustained unresponsiveness. Immunotherapy can be particularly helpful in removing some of the anxiety of inadvertent exposure. A doctor can talk you through the risks and benefits of this treatment and determine if it might be a good option in your particular situation.
But isn’t it better to just avoid everything I’m allergic to?
While avoidance does prevent symptoms, in some cases it may not be the best course of action as it can increase the severity of an allergy. Intake of an allergy-inducing food over time can lead to tolerance by increasing the formation of IgG antibodies, which block IgE. Therefore, regular consumption may protect against anaphylaxis. However, complete avoidance is still the best course of action in many acute cases. Your exact circumstances should be discussed with your doctor.
How exactly do IgG fit in?
IgG are our most prolific antibody defenders. They are found throughout the body and fight diligently against bacteria and viruses. In the intestines, they form for individual proteins when these proteins penetrate the intestinal lining. This most often happens when there is inflammation present, and the lining is compromised. Unlike IgE, significant amounts of IgG specific to food ingredients are normal in all individuals, and IgG antibodies are not associated with hypersensitivity reactions. In fact, they are essential to developing tolerance to food allergens. Since their presence is ordinary and not correlated with allergies, IgG tests should not be used to diagnose allergies. Interestingly, although IgG are largely beneficial, some studies have indicated surplus levels may be associated with chronic intestinal inflammation.
What is an elimination diet?
An elimination diet can be used to evaluate if a certain food or foods is causing or worsening a condition like atopic dermatitis. These diets may make getting nutrients difficult and are often only prescribed temporarily.
What about medications?
Drugs are available that may have an impact on food allergies. These include antihistamines, steroids, anti-IgE compounds, and antileukotrienes. From basic Benadryl to prescription medications like Omalizumab, which binds to IgE, you’ve got some options.
What will the future bring?
While the testing and treatment routes presently available for food allergies are perhaps less than ideal, the future may be more inspiring. More accurate testing methods are in their early stages. For instance, research has shown the basophil activation test (BAT) can differentiate between allergies and tolerances in sensitized foods. Additionally, allergy vaccines are being researched and developed. Vaccines work by inducing the creation of IgG antibodies specific to particular food allergens, which leads to tolerance. These could potentially be administered to pregnant women or at-risk infants. Scientists have also been undertaking the challenging task of designing processing and genetic manipulation to decrease the allergenicity of food. As an example, enzyme treatment has successfully been used to diminish the allergenicity of proteins such as gluten.
Like figuring out what triggers tantrums in two-year-olds, understanding more about what’s behind your body’s overblown reactions can help you manage them better. I wish you the greatest success in deciphering and dealing with the hypersensitive. May your IgE antibodies take up knitting or yoga instead of taking to drama.
References:
1. Anvari et al. (2018). The Nuts and Bolts of Food Immunotherapy: The Future of Food Allergy. Children, 5, 47.
2. Begin et al. (2013). Diagnosis of Food Allergy. Pediatric Annals, 1, 42(6), 102-109.
3. Gocki and Bartuzi. (2016). Role of Immunoglobulin G Antibodies in Diagnosis of Food Allergy. Advances in Dermatology and Allergology.
4. Manea et al. (2016). Overview of Food Allergy Diagnosis. Clujul Medical, 89(1), 5-10.
5. Masilamani et al. (2012). Determinants of Food Allergy. Immunology and Allergy Clinics of North America, 32(1), 11-33.
6. Mills and Shewry. (2004). Plant Food Allergens. Blackwell Publishing.
7. Thomsen. (2015). Epidemiology and Natural History of Atopic Diseases. European Clinical Respiratory Journal.
8. Valenta et al. (2015). Food Allergies: The Basics. Gastroenterology, 148(6), 1120-1131.