The first step in the diagnosis of allergic diseases is the assessment of a patient’s symptomatic history by an allergologist (a practitioner specialized in allergy diagnosis). This is called anamnesis. Important elements of this examination include an evaluation of the nature, duration, and time course of symptoms; possible triggers for symptoms; response to medications; family history of allergic diseases; environmental exposures; occupational exposures; and effects on quality of life. Once the possible causes of allergy have been narrowed down, there are 2 possible ways of confirming the actual disease-eliciting allergens: One includes the direct exposure of the patient to the allergen(s) in questions (so–called in–vivo tests) while the other employs a patient’s sample (such as blood or serum) to detect specific antibodies present in the immune system.

Laboratory investigations (In Vitro Test)

Diagnostic procedures conducted in a laboratory are based on detection of specific IgE antibodies in the blood or serum of allergic patients. Therefore, the corresponding methods can only diagnose Type-I allergic diseases. A major benefit of blood/serum testing is that a direct contact of a patient with allergen is avoided, which particularly relevant for the diagnosis of infants. Scientists have shown that the amount of total IgE present in the immune system of allergic patients is a reliable marker of allergy while it also indicates the severity of the disease. Typically, above average levels of IgE are reliable predictors of allergy. However, some patients don’t have elevated IgE concentrations although they are presenting with symptoms while others show high IgE levels but no history of allergic disease.
Once elevated IgE levels indicate allergy, possible disease-eliciting antibodies present in the immune system of a patient can be determined. Most conventional in-vitro diagnostic tests employ the well-known principle of solid-phase immunoassays to capture and quantify disease-related antibodies. In brief, allergen material (e.g. an extract from pollen, dust mites or cat hair) is immobilized on a solid substrate such as a microtitre plate or a nitrocellulose membrane. Subsequently, bound allergen material is incubated with patients’ serum in order to specifically capture and retain antibodies on the solid phase. In a washing step, excess serum components and unbound antibodies are removed. Afterwards, specifically retained IgE antibodies are detected using antibody conjugates carrying a fluorescence or radioactive label.

Patient Investigation (In-vivo testing)

Provocation Test

With this test the reaction of a single organ concerning an allergen is specific targeted.
Therefore the allergen is applied on the nasal mucosa or the conjunctiva, or the allergen will be inhaled. A provocation test may lead to heavy allergic reactions and perhaps to an anaphylactic shock!

Skin Testing (Prick Test/Patch Test)

The most important diagnostic procedure employing a direct exposure of a patient to a particular allergen source is the so–called skin-prick test (SPT). For SPT minute amounts of defined dilution of an allergen extract is applied to the skin of a patient (in most cases the forearm). The skin is then pricked through the drop using the tip of a lancet. When the allergen is introduced into the skin on a previously sensitized individual, IgE molecules on the surface of a mast cell cross–link and mediators of allergy (e.g. histamines) are being released. With a positive reaction to an allergen the skin becomes itchy within a few minutes and then becomes red and swollen with a ”weal“ in the centre (very much like the reaction to a nettle sting). With SPT, a number of allergens can be tested simultaneously when applied to different sections of the skin. Skin prick testing is a cheap, rapid and accurate way of identifying the causative allergens in a patient. Although these tests are generally accurate, there are some medications that can affect the results. When taking antihistamines patients are normally asked to stop taking these at least 48 hours before the test. Some other medications such as antidepressants can also interfere with skin prick tests. More importantly, where there has been a clear anaphylactic (shock) reaction to a specific allergen then skin testing is not appropriate. For these reasons it is sometimes better to rely on laboratory tests for the determination of allergen-specific IgEs instead!

Patch testing

The presumably allergen is patched on the back of the body and fixed for 48 hours. The reaction of this test is controlled after 48 and 72 hours. In case of a sensitization the skin is reacting in a period between 5 and 20 minutes.
It becomes red and swollen with a “weal” in the center (very much like the reaction to a nettle sting). In some cases this test has to be repeated several times and it faces always the risk of an anaphylactic shock!

Anaphylactic shock

The anaphylactic shock is the worst case of an allergic reaction. In that case vitally important organs are effected and in case of a circuit loss it may be even deadly.
What are the main triggers?
Insects: Bees, wasps, hornets
Antibiotics: i.e. Penicillin
Food substances: seafood, peanuts, celery, sometimes milk, wheat flour
Many other substances like pollen, animal hair, nuts, fruits, pain reliever, or latex may lead to an anaphylactic shock but not as heavy as mentioned above.
How an anaphylactic shock does occur?
The main reason is a substance called histamine. If the organism is getting in contact with the allergen it is reacting with histamine is set free. It may be even applied by consuming alcohol i.e.

How does the anaphylactic shock manifest itself?

Histamine leads to a higher permeability of the blood vessels.
The consequences are:
Primarily skin-flushing, itching in the mouth, on the palm of the hand, scalp or genitals.
Followed by dizziness, qualm and vomiting, sweating, breathlessness and finally unconsciousness and eventually death.

How are allergies treated ?

A simple way of treating allergic diseases is to avoid the contact with the disease-eliciting source. While this is sometimes possible in the case of certain food allergens, allergen avoidance is difficult to administer when a patient is plagued by pollen or dust mite allergies.
Nevertheless, a number of possible treatments are available. The goal of SIT is to “re-program” the immune system, therefore gradually diminishing the allergic symptoms or even completely eradicating the disease. Allergen immunotherapy involves injecting increasing amounts of an allergen to a patient over several months. Immunotherapy has been shown to prevent the development of new allergies and, in children, it can prevent the progression of the allergic disease from allergic rhinitis to asthma. Allergen immunotherapy can lead to the long-lasting relief of allergy symptoms after treatment is stopped. However, SIT has only proven effective in a limited number of patients and for a small number of allergens. Amongst others, this can be due to a lack of standardization of the extracts used for desensitization or a poly-sensitized patient not being treated for the major allergens causing his symptoms. Above all, scientists have found out that patients can gain novel allergies in the course of immunotherapy.
A possible alternative to SIT is pharmacological treatment, e.g. using anti-histamines to alleviate the symptoms of hay-fever. The gold-standard in the treatment of asthma are glucocorticoids (e.g. cortisone), mostly directly applied to the lungs using sprays.

Why is it important to pinpoint the allergy eliciting molecules ?

In order to design effective strategies for allergen avoidance and risk management in food allergy it is important to exactly identify the disease eliciting molecule. Particular allergens in certain foods (e.g. peanuts) have been shown to cause severe and life-threatening symptoms while others only lead to mild and localized reactions. The information provided by ISAC permits the sub-classification of allergens into groups of major and minor risk, hence facilitating the design of an individualized avoidance and risk management strategy for each patient. This is particularly relevant for children with food allergies.
Most importantly, tracing allergy at the molecular level improves the design of an optimal allergen cocktail for treatment with specific immunotherapy (SIT) (e.g. in pollen allergies). First, ISAC permits the identification of minor and major allergens present in different biological sources. Major allergens are molecules that have been shown to bind specific antibodies in a majority of affected patients (e.g. Bet v 1 in birch pollen), therefore posing a major risk in epidemiological terms. Therefore, allergen mixtures produced for the purpose of specific immunotherapy (-> see below) are typically standardized for these allergens with respect to relative concentration. However, patients who are exclusively reacting against a minor allergen risk being treated with an allergen cocktail not adequately representing their sensitization profile. Knowing the exact disease elicitors on a molecular level greatly facilitates the design of adequate treatments, either based on allergen avoidance or custom fabrication of desensitization cocktails for individual patients.
Furthermore, the component-resolved diagnosis (CRD) provided by ISAC facilitates the identification of possible cross-sensitizations to allergens in unrelated biological sources. Clinically, this type of reactivity to a number of structurally related proteins is caused by the promiscuous binding of IgE antibodies and is difficult to diagnose when using state-of-the-art extract-based test systems.
Example 1: Patients sensitized towards birch pollen frequently present with allergies against certain fruits or vegetables (e.g. apple, celery, or peach), based on the presence of particular cross-reactive allergen in birch pollen called Bet v 1 (see ISAC list of allergens for details).
Example 2: Patients allergic to dust mites frequently display cross-reactivities to seafood, snails or other insects, a reaction based on the binding of IgE antibodies to an allergen called Tropomyosin (see ISAC allergen list for details).