Gentowa

How does the skin test reaction look like?

The applied allergens are bound on the antibodies molecules IgE - on the outside part of the mastocytes and through the transfer of the signal their degranulation and the allergic reaction mediators release occur. These initiate the reaction through the affect on the surrounding blood vessels, the symptoms of which are the flush, the itch and the swelling with the diameter of several millimetres in the place of the injection. On the reaction, which starts approximately after 5 minutes from the allergen application, takes part also the so called substance P, which is released from the sensitive nerve ending, after the histamine stimulation. The reaction culminates in the period of 15-20 minutes, when the doctor subtracts it, after this time the reaction decreases.

The skin test realisation is not painful for the patient. On the palm side of the forearm the drops of the examining allergens are applied. In every drop a gentle puncture with the plastic or metal tool with the small sharp top is made. The skin is punctured only on the top skin layer so that the place does not have to bleed at all. After 20 minutes the reaction is judged. Places, which are either red or swollen in the same way as after applying the histamine, indicate that the reaction is positive. The patient can react to one or ore allergens. Beside the reaction when the small papule with the diameter of several millimetres appear, which is the most common reaction, the more extensive local reaction – of several centimetres, in rare cases even the swelling of the hand come about. These reactions cease to occur spontaneously after several hours.

In addition to the immediate reaction the patient can react in the so called later phase, when the papules appear after several hours. The patient deducts and informs the doctor of the reaction by himself/herself. The skin tests represent the allergist diagnosis basis. Together with the detailed taken anamnesis they are sufficient for the majority of the patients sensitive to common inhalation allergens for the typical symptoms of the diagnosis. Their role in the diagnosis is hence important, which relates to the fact that their preparation and realisation should be paid attention to.

The skin tests can be characterised as indirect provoking tests. They are called indirect, since their positives and negatives prove the sensitization of the human body. The presence of the specific IgE antibodies to applied allergen is proved on the skin without giving the information on the reactivity of the particular target organ (unless the target organ is the skin itself). Standard prick tests are used. They are made by the pharmaceutical companies, which prepare them according to the strict formulas. The content of all solutions with the allergens is diluted exactly together with the known analysed components of the particular chemical. The food allergens to the prick tests are chosen similar according to the patients. In the basic scale the eggs, nuts, milk and hesperidium should not be omitted. As far as the patient has not only a food allergy, but also the inhalational allergy, we add the cross reacting foodstuffs (birch-apple, Artemisia-celery, mites-crabs, latex-banana, etc.).

The professional airways allergic illnesses have increasing tendency. The allergens are represented by the whole range of various factors of both, the vegetable and animal origin, but also by the chemical agents. Besides the pharmacotherapy, which does not differ from the common recommended procedures, the fundamental step is the immediate transfer of the patient from the exposition of the cause, which is necessary to be defined. To the testing process the chemicals, which are not tested with the traditional patients, are added, as well.

The contact allergy diagnosis skin tests are made by putting the analysed chemical on the skin. More information is provided in the chapter about the contact allergy.

The laboratory tests are the necessary part of the diagnosis procedure, in the case that the previous examinations were not sufficient for the unambiguous conclusion. The important restriction of these tests is the fact that the patient’s allergic reaction includes different cells in different tissues of the high degree of the variability. Even in the case of the same patient the ability to react can change in a short period of time. For the sake of the laboratory examination the blood is necessary. The blood collecting is usually made in the morning. If we undergo the blood collecting, we will have to take into consideration that it will contain the small amount of the elements, which are influences by the food we have eaten. Hence the blood collecting should be undertaken not only on an empty stomach, but even in during the last evening before the collecting, the patients do not have to eat a fair amount of the fatty meals.

The leukocyte differential calculus belongs to the basic laboratory examination. The medical finding of the eosinophilia is typical as for the allergic patients. To the standard examinations belongs the total IgE level examination. The values above 100 IU/ml state the allergic reaction (illness). A reliable source of information is provided in the newborn umbilical cord examination, where the higher level above 10IU/ml reflects the higher risk of the allergic illness during the life.

The specific examination, which proves the allergy and analyses the initialising allergen, is the specific IgE antibodies examination. Here, the antibodies, which react against the particular allergen, are looked for and determined.

All the IgE determining methods are demanding and require special devices, hence are made only in bigger centres. They are not made to all patients. They are needed in cases, when the previous examinations did not prove the clear diagnosis. Moreover, even more simple methods using the testing slips of paper similar to the litmus paper are used in order to diagnose the IgE antibodies quantitatively.

Before the allergist examination all allergic patients should have examined the basic biochemical parameters, which are necessary for the therapeutic preparations. When needed, if we suspect the nasal cavity inflammation or the asthma, sometimes the X-ray examination is made. The X-ray pictures of the head, eventually of the lungs, where inflammation changes can be observed, are judged. The lungs and nose function is judged through the spirometric examination.

The skin tests are necessary supplements of all basic allergist examinations. The allergichypersensitiveness proof was discovered by Charlie Blackley already in 1865. The techniquewas later on improved by Grant Lewis, Pepyes and others, who introduced the prick test (stinger) usage. Nowadays the standardized method introduced by the European allergist andclinical immunology academy. The skin test in based on the fact, that sensitive allergic patient has specific antibodiesagainst the allergens not only in the particular organ, in which the clinical symptoms areactive, but also in the cell membrane – mastocyte which are in the skin.

While testing, the suspect allergen is injected into the patients´ skin near the forearm.

 The allergen choice is made according to the patients´ data on the clinical symptoms period.

The standard group of allergens, which includes the following, is used:

 ● trees pollen

● grass pollen

● rye

● worm wood

● ambrosia

● mould

● feather

● mites

● positive control (histamine)

●negative control (usually a solution with dissolved allergens)

According to the seasonality, others allergens are added. If the patient is in the contactwith the animals, the animal allergens (dog, cat, etc) are tested, as well. Before the testing thepatient should cease the anti allergic treatment (the antihistamines for at least one week), butothers, as well. For example many preparations used by the psychiatrists relieve even the skin reaction at the skin tests.

When possible, the patient should be tested even off pollen season. It is notappropriate to test somebody during or right after the infection since it can cover the reaction,as well.

For checking the skin test realisation correctness beside the allergens, the positive andthe negative control is injected. As the positive control histamine is used – a chemical, whichis released during the allergic reaction in general, i.e. test with this chemical can be positiveeven in the case of the health people. If this reaction after the testing is negative, the test is notvalid, since some of the processes or the medications relieved all reactions.The negative checking is, on the contrary, is injected in order to exclude the reaction,which is only mechanical – the injury or the injection itself, or the allergic reaction to thesolution, eventually to the conservative chemical in the allergen solution.

The skin tests allergens are made commercially. Their content and dilution are standardised.