Food Allergy and Intolerance Testing
A common food allergy test, in commercial use, measures IgG in the blood.
Kleine-Tebbe et al note that, whilst many of these samples show positive IgG4 results, there are no corresponding clinical symptoms. This, combined with the lack of convincing evidence for histamine-releasing properties of IgG4 in humans, and the lack of any controlled studies on the diagnostic value of IgG4 testing in food allergy, call into question the value of these type of tests.
They argue that food-specific IgG4 does not indicate (imminent) food allergy or food intolerance. What it does indicate is a physiological response of the immune system to food components.
They conclude that these type of tests should not be used to identify food related problems.
It would seem that presence of IgG4 may only indicate that you have recently eaten the food identified and that your body has reacted as expected.
One of my concerns with these tests is that some people come away with a very long list of foods to be avoided. If they avoided all of these foods their diets would be very restricted. My own view is that, if this type of test is used as a diagnostic tool, it still needs to be followed up by individual testing of the identified foods (by eliminating the food and then reintroducing it) to confirm whether they are in fact causing a problem.
For more information see my article on Food Intolerance testing.
J. Kleine-Tebbe, I. Reese, B. K. Ballmer-Weber, K. Beyer, S. Erdmann, Th. Fuchs, M. Henzgen, A. Heratizadeh, I. Hutt egger, L. Jäger, U. Jappe, U. Lepp, B. Niggemann, et al
No recommendation for IgG and IgG4 testing against foods
Allergo J 2009;4: 267