If an allergy appears, the search for the causing allergens requires detective work. First, there is the question whether a "real" allergy is present before the search for the allergens begins. Not every form of intolerance is an allergy.
The search for the allergens is very important.
From the huge range of substances in our environment, in food and also drugs, the right allergens need to be found. This is highly relevant for a successful therapy. For example, if a relatively harmless hay fever is not treated specifically, it may worsen, forming asthma, which is a serious illness.
What distinguishes a "true" allergy from a pseudo-allergy?
Physicians interpret an allergy as a hypersensitive reaction of the body to certain substances with an immunological background. That means, that with a “real” allergy the body's immune system is involved. In contrast, the immune system plays no role in pseudo-allergies. But the symptoms of pseudo-allergies are similar to “real” allergy symptoms.
What role do the allergens play in an allergy?
With an allergy, certain substances, the allergens, trigger a reaction from the immune system. These lead to the allergic symptoms, such as nasal itching, a skin rash, but may also lead to a life-threatening anaphylactic shock. In this case, the immune system should actually be defending the body. A healthy immune system is able to distinguish endogenous and exogenous substances reliably, so that pathogens can be tackled effectively. In case of an allergy, this process is malfunctional. Harmless substances in the environment such as pollen or even certain foods release mistakenly an exaggerated immune response. It's practically like cracking a nut with a sledgehammer.
How do allergens cause the symptoms?
The decisive factor is the binding of allergens to certain proteins of the body, the immunoglobulins (antibodies). Through the binding, a cascade of metabolic reactions is initiated that ultimately cause the symptoms.
The most common form of allergy is the "immediate type allergy" (type I allergy). The symptoms occur immediately after exposure to the allergen. The allergens are bound by antibodies which belong to the immunoglobulin class E (IgE). Because these antibodies recognize very specific allergens, they are called specific IgE antibodies. This knowledge is used for allergy testing (see below).
How can the disease-causing allergens be found?
Usually the medical history of a patient provides a very good indication of the possible triggers for an allergy. If, for example the complaints occur only during springtime, much could be said for an allergy to pollen from plants that bloom at that time. Year-round complaints however indicate allergens that are present throughout the year, such as dust mites or hair from pets. If the symptoms occur after eating a specific food, most likely that food is responsible. Each clue will help pinpoint the suspected allergens. Then, using various test methods, the relevant allergens can be determined.
Which diagnostic tests are available?
Often skin tests are performed, such as the so-called "skin prick test." In this case, the skin is scratched and a drop of allergen solution is applied. In an allergic reaction occurs, then the skin will show signs of irritation.
The allergens can also be found with the help of a blood sample, the serological test. The specific IgE antibodies, which are located in the blood serum can be determined in the laboratory. If, for example, antibodies against birch pollen can be detected in blood serum, this may be a good indication of a birch pollen allergy. The most common detection method is an immunological test called ELISA (enzyme-linked immunosorbent assay).
In addition, there is the provocation test. The patient is intentionally exposed to the allergen in order to provoke an allergic reaction, for example by placing a potential allergen in the nose.
When does each test make the most sense?
Skin tests are performed in many practices. But unfortunately, the results are often inconclusive and the interpretation requires great allergy experience from the physician. In particular, the reaction to food is difficult to diagnose. Many patients, especially children, find the skin tests unpleasant and stressful. For the serological test, blood only has to be taken once. Then the test is performed in laboratory machines (for example, in the HY · TEC from the company HYCOR Biomedical) and is fast and reliable.
The provocation test can be very stressful and risky for the patient. It may not be performed on pregnant women. It may only be preformed in rare cases where there is no other alternative.
What can a serological test say?
With the aid of a blood sample various allergens can be tested in the laboratory. Positive results give the doctor a clear indication of an existing allergy. The more specific IgE antibodies that are found in the blood, the more pronounced the allergy is. If the results are negative, a type I allergy is not likely. But to be on the safe side, usually the total amount of IgE antibodies is checked in blood serum. The total IgE level can provide an important indication for evaluating specific IgE results.
The allergens are found and what do we do now?
If the allergy-causing allergens are known, then targeted therapeutic action can be taken. Possiblities are a treatment with drugs, an allergen avoidance or desensitization - whichever is most appropriate for the allergy.
The most inexpensive would be a successful desensitization. In this case, the patient is given a very low dose of the allergen on a regular basis and if the therapy is effective, then the patient will no longer have an allergic reaction when exposed to the allergen.The success of treatment can be monitored by means of checking for antibodies in blood serum. Unfortunately, this is only possible for specific allergens.