RAST test

In addition to the exact anamnesis with the help of the diet diary and skin testing, blood tests also play an important role in the diagnosis of a food allergy. An essential part of this blood test is the so-called RAST test. RAST stands for Radio-Allergo-Sorbent-Test.

Blood is first drawn from the patient. The blood is then brought into contact with various antigens. These antigens are small amounts of substances that are potentially allergenic.

Thus, if hay fever is suspected, pollen particles are used as antigens. If animal hair or house dust mites are suspected, these are particles of animal hair or house dust mites. If a food allergy is suspected, particles of various foods such as nuts, dairy products or chicken egg protein are used as antigens.

If the body reacts particularly sensitively, i.e. allergically, to one of these antigens, this is indicated by the fact that certain antibodies from the patient’s blood bind to the appropriate antigen. This is made visible in the laboratory by a color marker. If antibodies from the patient’s blood bind to certain food antigens, this indicates the presence of an existing allergy to these antigens.

The RAST differentiates how high the concentration of these antibodies is in the patient’s blood. In this way, it is possible to specify more precisely how strong the sensitization of the body to the antigen in question is. The antibodies tested by the RAST test are class E antibodies, also known as IgE. This topic may also be of interest to you:

Allergy emergency set

How can I test a delayed food allergy?

In recent years and decades there have been repeated discussions about whether there are different types of food allergies. The classic food allergy belongs to allergy type I, also known as allergy of the immediate type. This allergy type is mainly mediated by IgE antibodies, which lead to a rapid activation of the immune system.

The typical allergic symptoms usually appear within a few minutes. It is discussed that besides this immediate type food allergy, there are also delayed type food allergies. This type of allergy belongs to allergy class III and is characterized by the formation of immune complexes, which are mainly mediated by IgG antibodies.

So far there is no sufficient study situation to make evidence-based statements about the actual existence of delayed food allergies. The problem in case of an actual existence of such a type of food allergy would be that the conventional tests, namely the prick test and the RAST test for IgE-antibodies could not sufficiently detect this type of allergy. There are therefore special tests for the detection of IgG antibodies in suspected food allergies of the delayed type. Due to the lack of studies on this topic, no reliable recommendations for the performance of these tests can be given at present.