Diagnosis

When diagnosing food allergy, a detailed medical history is of utmost importance. A diary can be helpful in this process, in which eaten foods and complaints of the patient are documented. It is also important to remove the suspected food from the diet for a while.

The symptoms should subside within 2 weeks. Your family doctor, dermatologist or allergologist can use a skin test (prick test) to check your suspicions. In rare cases, a so-called provocation test can be used.

In the provocation test, the body is provoked, so to speak, which means that the intolerant food is explicitly consumed. It is important that this only takes place under medical supervision, as it can lead to severe anaphylactic reactions that can be fatal. Normally, a food withdrawal test should be sufficient to diagnose a food allergy: This means avoiding the suspected food for a while and analyzing whether this avoidance has a positive effect on the allergic symptoms.

If this method does not give a sufficiently good result, a blood test can also be performed. For this purpose, the blood of the affected person usually has to be sent to a laboratory, where it is then examined for so-called type E immunoglobulins. These immunoglobulins play a crucial role in the development of an allergic reaction, and there are also specific immunoglobulins of this type for different molecules, if an allergy to these molecules is present.By determining these subtypes of immunoglobulins, a food allergy to certain foods can then be confirmed.

The diagnosis of a food allergy can be made in different ways. The simplest, but at the same time the most effective way, is to keep a diet and complaint diary. This makes it possible to establish a direct temporal connection between the consumption of a potentially allergenic food and the subsequent signs of disease.

If a certain food is suspected to be the trigger of an allergy, a several week exclusion diet with subsequent provocation diet follows. A further option for diagnosing a food allergy is the performance of various tests. The so-called prick test, which is also used for other forms of allergy, is very common.

Here, special solutions containing the suspected allergens are dripped onto the skin and placed under the epidermis of the skin with a lancet. At the same time, so-called empty tests are performed, in which a positive control is performed by introducing histamine and a negative control by introducing a pure saline solution into the skin. The first skin reactions can be assessed after only about a quarter of an hour.

In the case of a positive reaction, localized redness typically occurs, which is limited to the test area. The third common method used to test for a food allergy is blood testing. The simplest method is to simply test for free IgE antibodies.

This subgroup of antibodies is especially produced in the context of allergic reactions and parasite infestation of lymphocytes. However, this poses the problem that false positive test results can be obtained if the test person is infected by a parasite such as a tapeworm. Also, certain hematological diseases such as IgE-plasmacytoma can lead to an increase in IgE levels.

However, nowadays allergen-specific IgE antibodies can also be measured and their values cannot be falsified by other diseases. In addition to these laboratory tests, a wide range of novel blood tests for the diagnosis of food allergies is now available. In addition, the well-tried measurement of various inflammation parameters of the blood is still used.

The tissue hormone histamine, which is secreted in the course of an allergic reaction and is responsible for many of its symptoms, should be mentioned first and foremost. The enzyme tryptase and the so-called leukotrienes are also elevated in an allergic reaction, so that they too can provide information about the general presence of a food allergy. It should be noted, however, that blood tests are also available, which in themselves are not suitable for diagnosing a food allergy. For example, the German Medical Journal (Deutsches Ärzteblatt) was very critical of the so-called ALCAT test procedures, which are based on the determination of non-allergy-specific IgG antibodies.