Food allergy testing with IgG4 is not recommended

Food allergy and intolerance can be clinically challenging to nail down, and clinical experience over the years compelled me to accept the unreliability of food allergy tests that depend on IgG4 antibodies. Foods reported as allergic were well tolerated by patients, and significant foods were missed. Judging from the lab results patients bring from elsewhere it appears that IgG4 antibody screens for delayed food allergy remain widely in use. Practitioners should note a paper published in the journal Allergy that explains why they are not recommended for clinical use. The authors state:

"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."

They point out that the mechanism by which IgG4 acts in food allergy is questionable:

"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."

Moreover, IgG4 antibodies act to promote tolerance to foods:

"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."

A lack of dependable food allergy tests drove me to abandon them and resort to the venerable elimination-provocation procedure, but this of course has limitations. Since then I have found a reliable laboratory resource that offers more advanced, clinically significant results. I encourage practitioners to consider the authors' conclusion:

"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."