May is Food Allergy Action Month, so we thought we’d take some time to outline your options in regards to food allergy/hypersensitivity testing. With so many choices out there, knowing the pros and cons of each testing method can help you decide which test is right for you.
Food Allergy vs. Food Hypersensitivity vs. Food Intolerance
First things first, based on conversations with thousands of clients as well as clinicians, there is a lot of confusion about the difference between a food allergy, a food hypersensitivity (often called a delayed-onset food allergy) and a food intolerance, so let’s clear that up.
A true food allergy results when the body releases Immunoglobulin E (IgE) in response to a food; this results in the immediate release of histamine from immune cells (called mast cells) and can result in symptoms ranging from minor itching and swelling to severe, possibly life threatening swelling of the tongue and throat.
A food hypersensitivity is a non-IgE immune reaction to a food. The immune system can have an immune reaction to a food (or other substance) that does not involve IgE, but rather one of the other immunoglobulins (especially IgG and IgA), T-cells or immune complement reactions. These reactions are usually less severe than an IgE response and can take up to 72 hours to present themselves, which can make food hypersensitivities difficult to determine without testing.
A food intolerance does not involve the immune system; instead it is a reaction caused by incomplete or improper digestion, assimilation and/or elimination of a substance. Lactose intolerance is the best studied example: an inability to properly digest lactose causes intestinal irritation that can cause a multitude of symptoms, including constipation, gas, bloating, diarrhea and abdominal distention. Intolerance reactions are difficult to measure, as there are only a few assays available and are usually determine through trial-and-error.
Now that you know more about the different reactions the body can have in regards to food, let’s take a look at the tests that are available.
Food Allergy & Hypersensitivity Testing
There are really just two broad categories of tests to measure an immune response to food: tests of classic allergy and tests of hypersensitivity.
Tests of classic allergy measure IgE either by RAST (radioallergosorbent test) blood tests or by in-office skin prick tests. These are also called Type 1 hypersensitivity (or immediate hypersensitivity) reactions and are usually (the only testing) conducted by medical clinics & hospitals. While it is very important to know if you have IgE reactions to foods, IgE reactions represent only a small percentage of immune reactions to foods; therefore further evaluation using tests of food hypersensitivity are necessary to determine the full extent of any food-based immune reactions .
Tests of hypersensitivity measure non-IgE immune responses to foods. There are three mechanisms by which these reactions can occur:
- Reactive antibodies (IgA, IgM, IgG)
- Immune complexes
- T-cell mediated responses
These reactions generally occur several hours to several days after exposure, which can make identification of these substances difficult using standard methods like a food diary. However, these types of hypersensitivity reactions are usually the most clinically relevant, so accurate determination is essential to speed the healing process.
Food Hypersensitivity Testing
There are several methods that are used to measure delayed hypersensitivity reactions to foods and/or environmental allergens. The most common are serum tests of immune system memory, particle size tests and functional immune system assays. It is very important to understand the differences between these different testing methodologies in order to choose the test that provides you the data you are looking for.
Serum Tests of Immune System Memory
These tests measure the antibody levels – typically IgG or IgG4 – present in the serum after exposure to a food. ELISA, IgG and IgG EIA testing are good examples. The presence of antibodies reveals that at some time, the immune system mounted a response to a tested substance. However, even though some of these antibodies can provoke a negative reaction, not all these antibodies are bad; some can actually protect you. The inability to differentiate between the harmful, provoking antibodies and those that protect the body is a major drawback to this type of testing, as this can lead to an abundance of false positive results, making diets based on these tests overly restrictive.
In addition, IgG antibodies are only one class of delayed hypersensitivity reactions (albeit the largest one, accounting for an estimated 70% of delayed hypersensitivity reactions); therefore, these tests will also miss many offending foods or environmental allergens (i.e., have false negatives). Based on these facts, IgG testing can be of some value, but it’s utility is limited.
Particle Size Tests
These tests measure particles of a specific size (usually ten microns) that are present in serum exposed to specific antigens (i.e., foods). The theory is that because reactive immune cells have a size of approximately ten microns, measuring particles within this range can give an accurate approximation of the body’s reaction to a substance. The problem is that many other cells and substances in the blood can have a size of approximately ten microns, including clumps of platelets, stacks of red blood cells and pieces of old white blood cells, that can through off these measurements. Because there is no way to differentiate these substances from the reactive immune cells, these tests are not very accurate and can lead to results which are unnecessarily restrictive (i.e., falsely identify many foods/substances that don’t actually cause an immune reaction).
ALCAT and SAGE are both common labs that offer tests of particle size.
Functional Immune System Assays
These tests are also known as Lymphocyte Response Assays (LRAs) and identify the full range of delayed immune responses, including reactive (i.e., provoking/harmful) antibodies, immune complexes and direct T-cell responses to potential food and environmental agents. This makes the LRA one of the most comprehensive and clinically accurate assessment techniques currently available to target non-IgE-related allergens. This test is administered by Elisa/Act Biotechnologies: www.elisaact.com, and we have found it to be incredibly helpful with our clients, especially those that have conducted one or more of the previously mentioned tests.
If you suspect you are having immune reactions to foods, (1) speak with your medical doctor about conducting IgE testing and (2) find a provider that can help you determine which LRA test would be right for you. Once you have that information, your health care provider can tailor make a diet and supplement regime to help you heal the GI tract, calm the immune system and restore optimal health.