Thank you for your inquiry.
I believe that the best way for me to answer you is to refer you to four international consensus evidence-based guidelines from four sources throughout the world, each mentioning the validity of tests used to diagnose food allergy, including antibodies to foods other than those of the IgE class.
One of these is from the United States, one from South Africa, the third is from Europe, and the fourth from Australia. They all reach the same conclusion as expressed in the abstract which I also copied and sent.
I hope you will have a chance to read these and find them helpful.
Thank you again for your inquiry.
Allergy 2008: 63: 793–796 Ó 2008 The Authors Journal compilation Ó 2008 Blackwell Munksgaard
Testing for IgG4 against foods is not recommended as a diagnostic tool: EAACI Task Force Report*
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 hyper- sensitivity. 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 immu- nological 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 per- formed in case of food-related complaints.
Phil Lieberman, M.D.