Questions about Immunoglobulin G (IgG) testing come up quite often - I know of several physicians, chiropractors, and other health practitioners who, unfortunately, refer their clients for IgG testing when food sensitivities are suspected. If you've already had IgG testing done, I'm sorry to say that the results are not very helpful in identifying food-related reactions.
IgG production is a natural part of the immune response when the immune system is exposed to a food. Elevated IgG levels do NOT necessarily mean that the body is having a negative response to a food; elevated levels simply mean that the body has been "exposed", whether this exposure is good, bad, or otherwise (this, essentially, acts as a really expensive food diary, as it basically just shows which foods were eaten recently). This is why IgG testing is NOT recommended as a diagnostic tool (elevated IgG can actually indicate tolerance, not intolerance to a food).
American Academy of Allergy, Asthma and Immunology Support of the European Academy of Allergy and Clinical Immunology Position Paper on IgG4 - May 2010
The recent European Academy of Allergy and Clinical Immunology (EAACI) Position Paper by Stapel et al concerning testing for IgG4 against foods is a timely reminder that this issue is pervasive throughout the world. The ease of obtaining laboratory tests for suspected allergic symptoms, which then need sophisticated interpretation, is an ongoing problem. It should be stressed that the use of all tests for allergy should be supported by the scientific evidence base, when it exists. The improper use of certain tests to make diagnoses, in the absence of supporting clinical evidence, can lead to poor patient care and can have a serious adverse impact on patient quality of life.
The American Academy of Allergy, Asthma & Immunology supports the EAACI Position Paper, and without reiterating the entire document, the following points deserve emphasis:
1. It is neither possible nor appropriate to use serum antibody tests to diagnose food allergy in the absence of a good history and possible challenge testing.
2. Serum antibody levels for IgG4 or IgE (or other IgG subclasses) indicate the presence of specific antibody but do not make a diagnosis. The presence of antibody does not indicate disease
3. It is common for primary care providers to order serum antibody tests (usually IgE) for food allergy in the absence of a thorough history and without a skilled background for interpretation. These tests are often obtained as panels rather than being selected based on the history. The results may then lead to confusion when incriminated foods that are well tolerated by patients are removed from the diet. Well tolerated foods should not be removed from the diet even in the presence of positive tests.
4. Some practitioners order IgG and IgG4 antibody tests for foods and the results may be misinterpreted, leading to diets that may be nutritionally inadequate and are certainly not easy for patients to follow.
5. Commercial laboratories frequently offer these tests to all types of practitioners, and it is not unusual for their marketing and sales people to oversimplify the ease of interpretation of the tests.
6. The misinterpretation of IgE-mediated specific antibody tests could lead to serious reactions when an undetectable antibody level is interpreted as negative and the patient is told to consume the food, and then clinical symptoms occur, emphasizing the point that an undetectable result is not necessarily a negative result. These comments reiterate those of Stapel et al that the detection of food-specific antibody in patient sera does not necessarily indicate food allergy or intolerance, but rather a physiologic response of the immune system to exposure to food. For IgG and more specifically IgG4, this may be the normal human response. Although the detection of specific IgE antibody may indicate the potential for a reaction to occur, there frequently is no clinical consequence to the presence of these antibodies.
The following is a scientific abstract on this topic from the European Academy of Allergy and Clinical Immunology:
Serological tests for immunoglobulin G4 (IgG4) against foods are persistently promoted for the diagnosis of food-induced hypersensitivity. Since many patients believe that their symptoms are related to food ingestion without diagnostic confirmation of a causal relationship, tests for food-specific IgG4 represent a growing market. Testing for blood IgG4 against different foods is performed with large-scale screening for hundreds of food items by enzyme-linked immunosorbent assay-type and radioallergosorbent-type assays in young children, adolescents and adults. However, many serum samples show positive IgG4 results without corresponding clinical symptoms. These findings, combined with the lack of convincing evidence for histamine-releasing properties of IgG4 in humans, and lack of any controlled studies on the diagnostic value of IgG4 testing in food allergy, do not provide any basis for the hypothesis that food-specific IgG4 should be attributed with an effector role in food hypersensitivity. In contrast to the disputed beliefs, IgG4 against foods indicates that the organism has been repeatedly exposed to food components, recognized as foreign proteins by the immune system. Its presence should not be considered as a factor which induces hypersensitivity, but rather as an indicator for immunological tolerance, linked to the activity of regulatory T cells. In conclusion, food-specific IgG4 does not indicate (imminent) food allergy or intolerance, but rather a physiological response of the immune system after exposition to food components. Therefore, testing of IgG4 to foods is considered as irrelevant for the laboratory work-up of food allergy or intolerance and should not be performed in case of food-related complaints.
Another consideration with food sensitivity testing is that there are many possible mechanisms and cells that could be involved; we don't necessarily know which route will be involved for each adverse reaction... it could be IgG, IgA, IgM, C3, C4, T-cell activation, or others (IgG is just one possible part of the equation). Testing for just one component is not a particularly helpful way to pinpoint food sensitivities (it's like trying to put a puzzle together with most of the pieces missing).
Take migraines, for example - studies have shown that in most migraine cases, IgG has little, if any, role in adverse food reactions that present as migraines (T-cells and natural killer cells are typically involved in migraine cases).
The Mediator Release Test (MRT) excels where the other food sensitivity tests fall short - MRT is an endpoint test, meaning that it doesn't care which route was taken in the manifestation of food sensitivities; it measures the end result of these adverse reactions (inflammation).
If you’d like even more information on food sensitivities and testing, read “The Patented Mediator Release Test (MRT): A Comprehensive Blood Test for Inflammation Caused by Food and Food-Chemical Sensitivities,” by Dr. Mark Pasula (downloadable PDF file).