Testing for Food Allergies
Everything you need to know about IgE mediated allergies and testing
True allergies (environmental or food) result in an immunological reaction in the body resulting in common symptoms such as hives, skin rashes, swollen lips, eczema, stuffy nose, constant coughing and in rare cases anaphylaxis. A specialist in allergy and immunology is needed to properly diagnose an allergy and there are several methods of testing. Combining a patient’s history along with a measured reaction, a qualified doctor can diagnose an allergy. Allergies can also develop at any time, but are commonly discovered and diagnosed in children.
Skin Prick Test
This primary testing method involves individual needles containing a small amount of the suspected allergen that are then pressed into the skin. A reaction is determined by measuring the size of ‘wheal’ (a red, possibly itchy bump) that rises from the prick site. A very experienced doctor or nurse is needed to perform this test, as false positives can occur at rates of up to 50-60% if a less experienced professional presses the needle in too deeply, if a multi-prick device is used, cross-reaction within food families or the level of digestion of the proteins in the body. Multi-prick devices are not only dangerous (they can administer too many allergens at one time resulting in a possible severe reaction), but administering a panel onto an uneven surface will often give inaccurate results as some needles may go deeper than others. Make sure the doctor performs a control site so comparisons wheals are accurate.
IgE Antibody Blood Test
If any positive results are suspected from the prick test, the next test to be administered in the IgE antibody blood test. IgE antibodies are created in a cascade reaction when the body perceives an invader whether it is food or an environmental factor like pollen or dust. The process occurs when IgE antibodies bind to a specific type of cell called a mast cell. As explained on the Asthma and Allergy Foundation of America’s website, “The surfaces of mast cells contain special receptors for binding IgE. The IgE antibody fits to this receptor like a module docking with the mother ship.” When enough IgE antibodies ‘dock’ on the mast cells, the mast cells release histamine and substances/toxins that create inflammation. This is the first step in creating an IgE allergy and sensitizes the body to react in this way again when exposed to the substance. Exposure can happen through ingestion, inhalation, injection or exposure to a substance via the skin.
The blood test will reveal if there are elevated levels of IgE antibodies to a number of suspected foods or environmental substances. This is particularly a good test for children and adults who have had severe reactions in the past as no substances are put on or in the body.
It’s possible for an individual to receive false negatives on allergy tests, so often if a substance is strongly suspected but the results do not correlate, the health professional may suggest the intradermal test. This test involved a small amount of substance being injected, usually on the forearm, just beneath the skin. The site is then examined after twenty minutes. In some cases, the doctor will re-evaluate after a longer period of time such as 48-72 hours later. The intradermal test is more sensitive than the prick test and can provide more accurate results. It’s often used for suspected penicillin and bug bite allergies. Make sure the doctor performs a control site so comparisons are accurate.
In conjunction with the test options above, sometimes an individual is asked to completely avoid a specific food for 2 week to 3 months. After that time period, the food is reintroduced to see is symptoms or a reaction occurs.
Oral Food Challenge
A person is given small amounts of the potential allergen, most likely food, under medical supervision in an office or hospital setting to monitor potentially severe reactions. Oral food challenges are common after desensitization protocols, where an individual is given minute amounts of an allergen to desensitize the body to a potential food such as peanuts.
The Big Eight/Ten Allergens
The Big Eight causes approximately 90% of all allergic reactions. Recently, corn and sesame have been added, as rates of those allergies have risen.
- Dairy (cow’s milk)
- Tree Nuts
In Asia, according to this study (http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3563019/), “Shellfish is the most common food allergen from Asia, in part due to the abundance of seafood in this region. It is unique as symptoms vary widely from oral symptoms to anaphylaxis for the same individual. Data suggest that house dust mite tropomysin may be a primary sensitizer. In contrast, peanut prevalence in Asia is extremely low compared to the West for reasons not yet understood. Among young children and infants, egg and cow’s milk allergy are the two most common food allergies, with prevalence data comparable to western populations. Differences also exist within Asia. Wheat allergy, though uncommon in most Asian countries, is the most common cause of anaphylaxis in Japan and Korea, and is increasing in Thailand. Current food allergy data from Asia highlights important differences between East and West, and within the Asian region. Further work is needed to provide insight on the environmental risk factors accounting for these differences.”
IgE mediated allergies occur when the immune system develops an IgE antibody to a perceived or real foreign substance. The body then manufactures these antibodies, and when exposed again to the substance the antibody attaches itself to a special type of cell called a mast cell. As soon as the antibody docks to the mast cell, the mast cell undergoes a series of chemical reactions releasing a host of toxins and histamine. It is then you get the commonly known symptoms of hives, atomic dermatitis, rash, and so forth.
Labeling laws vary, and since Asia has a vast number of imports, it is a good idea to familiarise yourself with the basics. Below you can find labeling laws for the United States, Australia/New Zealand, the European Union and Hong Kong.
- UNITED STATES: RESOURCE HERE
- Manufacturers include allergy information in bold print using language such as Contains (allergens)
- You may also see advisory warnings such as Manufactured on equipment, Produced in a facility or May contain (allergens)
- AUSTRALIA/NEW ZEALAND: RESOURCE HERE
- Foods containing the Big Eight allergens must be labeled
- Gluten is also labeled for individuals with celiac disease. Gluten Free foods are labeled to a standard of less than 20ppm
- May contain, Manufactured on equipment using, and Produced in a facility are all voluntary statements.
- EUROPEAN UNION: RESOURCE HERE
- Big Eight allergens with clear labeling and emphasized by font style, old or background colour
- May contain, Manufactured on equipment using, and Produced in a facility are all voluntary statements. Work is being done to clarify the use of these statements.
- HONG KONG: RESOURCE HERE
- Labeling of the Big Eight plus sulphites over 10parts per million are required on food labels. There is no ‘tolerance’ level for allergens, as “the amount of allergenic protein necessary to elicit an allergenic reaction can be very small.”
- Allergens should have clear labeling with emphasized font style, use of parenthesis or specific language such as, “contains soy.”
New tests and information are coming out every year that provide more insight and hope for individuals with allergies. For example, according to Dr. Nigel Abraham, IgE antibodies protect the body from parasites and worms. There are theories suggesting that the absence of these animals have left our immune system in a ready-to-react-to-anything state. Recently in a study an individual was given a parasite and the IgE allergy disappeared, adding some credence to this theory. Other theories include less exposure to germs, gut health and genetic susceptibility. To read more about studies on these theories and about IgE, please refer to the following:
- Helminth Allergens, Parasite-Specific IgE, and it’s Protective Role in Human Immunity
- Allergy, Parasites and the Hygiene Hypothesis
- Helminth Infection Alters IgE Responses to Allergens Structurally Related to Parasite Proteins
- Gastrointestinal Food Allergies
- IgE-dependent signaling as a therapeutic target for allergies
- Allergy Testing in Childhood: Using Allergen-Specific IgE Tests