Allergen tests: how they do it. Allergy tests Skin tests for allergies in children

20.09.2023

Skin tests are included in the allergy examination program for patients of different ages. They are used to detect allergens that provoke pathological changes in the body and prescribe allergen-specific treatment.

The test consists of applying a small amount of the suspected allergen to a certain area of the skin and examining it by a doctor after some time. The occurrence of redness and swelling in this area is considered a positive reaction, indicating the body's sensitivity to the allergen. The resulting redness and swelling are assessed and measured to determine the degree of sensitivity to the allergen component.

There are several techniques for performing skin tests.

Scarification - tests involving scratching the skin.
Intradermal - the allergen is introduced into the upper layer of the skin.
Application - the allergen component is applied to the surface of the skin. These are closed and open patch tests used to detect delayed-type hypersensitivity in contact dermatitis.
Prick tests - piercing the skin with a needle (prick test).

The main indications for prescribing skin tests to a patient are:

bronchial asthma;
rhinitis that cannot be treated with medication;
suspected food, drug and insect (caused by insects) allergies;
atopic dermatitis;
acute and chronic urticaria, conjunctivitis (in children);
reactions to insect bites, anaphylaxis (in children).

Contraindications for patient participation in skin testing include:

extensive pathological changes in the skin;
urticarial dermographism;
severe somatic diseases in the stage of decompensation;
impossibility of discontinuing medications that may affect the results of allergy tests;
mental disorders;
age less than 2 years (due to difficulties in interpretation);
risk of developing anaphylactic shock;
pregnancy.

The term “allergy tests” or “allergy tests” refers to 4 types of tests:

skin tests,
blood test to determine the total level of immunoglobulin E,
blood test to determine specific antibodies,
provocative tests.

To make an accurate diagnosis, the results of one or two of the listed tests are required. The examination begins with skin testing. If there are contraindications, they resort to a safer diagnostic method - a blood test for antibodies. A provocative test for allergens is used only in extreme cases: if discrepancies arise between the results of studies already conducted and the patient’s medical history (for example, a survey shows that the patient is allergic to birch pollen, but skin tests do not confirm this).

Allergies to different substances most often present with the same symptoms. It is difficult to determine the cause of an allergy without using special skin tests, more commonly called allergy skin tests. This method is the most common in allergology, and is used to establish an accurate diagnosis.

Allergy tests are carried out for diseases such as:

bronchial asthma, manifested by repeated signs of suffocation as a result of spasm of the bronchi when exposed to allergens;
allergic dermatitis, characterized by rashes, redness and itching;
hay fever or allergy to pollen, which manifests itself as rhinitis, conjunctivitis, sneezing and runny nose;
food allergies, which are characterized by skin rashes, redness and itching.

How are skin tests done?

Skin tests for allergens can be done by scarification, with skin piercing (prick tests) and intradermal. In the first two cases, the procedure is quite simple. The doctor applies solutions of “interested” allergens to the skin of the patient’s back or forearm - no more than 15-20 per procedure. Under the drops, scratches are made using a special plate (scarification method) or shallow injections with a thin needle (prick method). You don’t have to languish in ignorance for long - the doctor evaluates the test results within 20 minutes.

Skin allergy tests are not performed:

during an exacerbation of any chronic disease (including allergies),
during acute infectious diseases,
children under 3 years old,
pregnant and lactating women.

In addition, it is not recommended for women to use this research method in the first days of the menstrual cycle. Due to hormonal changes occurring in the body, test results may be unreliable. In order to take an allergy test, the patient is asked to prepare in advance:

2 weeks before the procedure, stop taking internal antihistamines,

Stop using antiallergic ointments in a week.

Timely diagnosis of allergies is the main condition for its successful treatment and prevention of possible relapses. To carry it out, a comprehensive examination is carried out, an important component of which is allergy testing. Before the procedure, the doctor explains what allergen tests are, how they are done and how to prepare for them. However, it is advisable to study all the necessary information in more detail in order to obtain the most accurate test results and prevent complications from occurring.

Allergy tests are testing the body to determine individual intolerance or hypersensitivity to specific irritating substances (allergens). Such an examination is necessary in the following cases:

if there is a tendency to allergic reactions, to identify most of the possible allergens;
at the slightest suspicion of an allergy before administering anesthesia, prescribing new medications, using unfamiliar cosmetics or other similar situations, especially in children;
if you need to identify an allergen when the cause of the painful response of the immune system to the patient is unknown.

In addition, some diseases are indications for testing:

bronchial asthma with severe respiratory disorders;
hay fever with pronounced symptoms of its classic manifestation;
food and drug allergies;
, conjunctivitis, dermatitis.

Allergy tests allow you to quickly obtain the necessary information about which substance causes hypersensitivity. To do this, the body is exposed to small doses of various irritants, and then the result is assessed by the nature of the reactions.

Diagnostic methods

The most reliable method for identifying allergens is a comprehensive allergy diagnosis using a blood test. It allows you to simultaneously determine the body's sensitivity to 40 of the most common allergens of various types. This method may be the only possible one if there are contraindications to skin testing, but it is very expensive and inoperative.

Faster and more accessible are skin and provocative tests, with which you can check the immune system's reaction to a maximum of 20 allergens.

Skin allergy tests are classified according to several criteria.

According to the final result:

qualitative – confirm or refute the presence of an allergy to a specific substance;
quantitative - determine the strength of the allergen and its critical amount that can cause a negative reaction of the immune system.

According to the composition of the provoking substance used:

direct - carried out by applying or introducing pure allergen into the skin;
indirect (Praustnitz-Küstner reaction) - the subject is first injected with the blood serum of a person suffering from allergies, and a day later - the allergen.

By method of allergen administration:

application (patch tests) - to determine the majority of existing allergens;
scarification or needle tests (prick tests) - for seasonal allergies to plants, Quincke's edema, atopic dermatitis;
intradermal (injection) - to identify fungi or bacteria that have become the causative agent of allergies.

With any of these studies, some errors are possible due to external factors and characteristics of the body. To clarify the result if it does not coincide with the symptoms of the disease, provocative tests are additionally prescribed. They involve the direct impact of a provoking substance on the organ that has become the site of the allergic reaction.

The most commonly used tests are:

conjunctival (for allergic inflammation of the conjunctiva);
nasal (for similar inflammations of the nasal mucosa);
inhalation (for diagnosing bronchial asthma).

Other provocative allergy tests can also be performed - exposure or elimination (for food allergies), heat or cold (for a corresponding thermal rash), etc.

How are allergen tests done?

The procedure is performed by an allergist in a specially equipped room. He also evaluates the results obtained and makes an appropriate diagnosis.

Skin tests

Allergy tests of this type are carried out on healthy areas of the skin, most often in the forearm area, less often on the back. Each of the above procedures is performed in a special way:

Patch tests (patch tests) are performed using a gauze or cotton swab soaked in an allergen solution, which is attached to the skin using a patch.
Scarification or needle tests (prick tests) - involve the dropwise application of a provoking substance, followed by minor damage to the surface layer of the epidermis (light scratches with a scarifier or needle).
Intradermal tests (injections) are based on the administration of the drug by injection to a depth of no more than 1 mm. A white dense bubble with a diameter of about 5 mm immediately forms at the puncture site, which resolves within 15 minutes.

The results are assessed according to two parameters:

speed of reaction manifestation: instantly – positive; after 20 minutes – immediate; after 1–2 days – slow;
the size of the redness or swelling that appears: more than 13 mm – hyperergic; 8–12 mm – clearly positive; 3–7 mm – positive; 1–2 mm – doubtful; no change – negative.

The skin reaction is assessed on a scale from 0 (“–”) to 4 (“++++”), which reflects the degree of sensitivity of the body to the allergen.

Provocative tests

The methodology for conducting such studies depends on the location of the affected organ and the option of access to it:

Conjunctival test - carried out by first instilling a test control liquid into one eye, and if there are no changes within 20 minutes, then a minimal concentration of allergen solution is dripped into the other eye. If there is no reaction, after 20 minutes, the allergen solution is again instilled into the same eye, but with a concentration doubled. Such studies continue until there is no allergic reaction, constantly increasing the concentration by 2 times. Complete the test with undiluted allergen.
Inhalation test - carried out by inhaling an allergen aerosol in a minimum concentration, then the reaction of the respiratory system is monitored for 1 hour (after 5, 10, 20, 30, 40 and 60 minutes). If there are no changes in the rhythm, depth and purity of breathing, the test is repeated again with a twice as high concentration of the allergen and is also brought to its undiluted state.
Nasal test - performed in a similar way, but the corresponding liquids are instilled into one and the other halves of the nose.

An exposure test involves direct exposure to a possible irritant and is performed in cases where there are no pronounced manifestations of an allergic reaction. Elimination tests are also performed in the absence of symptoms, but using the reverse method - by refusing to consume a possible allergen product, changing the environment, discontinuing the drug, etc.

When choosing an allergen test option, it is necessary to consider all the pros and cons of each of them. Skin tests are fairly quick and simple, but are unsafe as they can aggravate allergies. It is also possible to obtain false results, which largely depend on the condition of the skin, the subjectivity of the assessment, and technical errors. In addition, such allergy tests have a number of contraindications.

Contraindications for staging

All types of allergy tests are not performed in the following cases:

exacerbation of allergies and for 2–3 weeks after it;
taking antihistamines and other drugs that suppress the production of histamine, and the first week after their withdrawal;
use of sedatives and other sedatives containing barbiturates, bromine and magnesium salts, and 7 days after stopping use;
exacerbation of chronic diseases, including neuropsychiatric disorders, or the recovery stage;
bearing and feeding a child, menstruation - in women;
previous history of anaphylactic shock;
taking hormonal drugs and 2 weeks after completion of the course;
the presence of infectious and inflammatory processes in the body (respiratory, viral diseases, sore throat, etc.), as well as intercurrent infections;
cancer, AIDS, diabetes;
the presence of an acute reaction to a specific allergen;
age up to 3–5 and after 60 years.

If there is any contraindication to skin testing, allergy diagnosis is performed based on a blood test.

Complications of allergen testing

The most serious complication after allergy testing can be caused by delayed-type hypersensitivity, which develops within 6-24 hours after the test. Its manifestations can be expressed by the following symptoms:

deterioration of health, the appearance of discomfort;
irritation and prolonged non-healing of the allergen injection site;
development of increased sensitization to the irritant or a new allergic reaction.

In some cases, on the contrary, there is no skin reaction, which does not allow identifying a specific allergen and obtaining a specific result from the test performed. Hypersensitivity to the test itself may also occur, the consequences of which can be unpredictable and very dangerous, including death.

How to prepare for tests

Preparation for testing for allergens should begin with an analysis of contraindications and the exclusion of all possible factors that could distort test results. It should also be taken into account that tests can only be carried out during stable remission, at least a month after the exacerbation.

In addition, the preparatory stage includes the following restrictions:

3 days before the examination you need to reduce physical activity;
1 day in advance - quit smoking;
on the day of testing - do not eat food, since skin tests are performed on an empty stomach or at least 3 hours after eating.

If you are prone to allergies, you need to take tests for allergens at least once in your life, as people who care about their health do. It is always easier to prevent any disease than to then eliminate its symptoms and consequences. This is especially important in cases of allergic reactions. After all, they can arise from completely unexpected irritants, knowing which, you can avoid contact with them and live your whole life without allergies.

Skin tests for allergens are a highly informative method for determining the irritant in case of hypersensitivity of the body. The technique is simple and effective, with minimal discomfort for the patient.

It is important to know the indications and contraindications for performing prick tests, prick tests and special applications. Rules for preparing for the study, the course of the procedure, types of reactions, results are described in the article.

Skin tests: what are they?

The technique allows you to determine the type of allergen and the type of negative reaction:

when an allergen comes into contact with the skin, interaction with mast cells occurs;
local allergic signs occur after the penetration of an irritant into a wound on the skin, with the release of serotonin and histamine;
in the area where an irritant dangerous to the patient is applied, the epidermis turns red, itches, papules often appear, the site of a scratch, application or injection swells;
Based on the results of the appearance of allergenic foci, doctors determine the types of irritants, contact with which will have to be excluded.

Mandatory elements of skin tests are solutions and extracts of various types of allergens. Doctors use glycerin and histamine to determine if the test is correct. A reaction to histamine occurs in most cases; the absence of even a weak response on the skin indicates possible errors in skin testing. To apply irritants, use a needle, lancet or tampon applicator.

In what cases are studies prescribed?

Indications for skin tests:

(hay fever);
intolerance to certain products and substances in food (lactose, gluten);

Contraindications

Doctors do not conduct testing in the following cases:

infectious diseases with severe course: bronchitis, sore throat, pneumonia;
the patient has been diagnosed with AIDS or autoimmune pathologies;
high risk of anaphylactic reactions;
lactation period;
decompensated stage of asthmatic disease;
pregnancy;
a malignant tumor has been identified;
exacerbation of allergic symptoms;
mental disorders.

On a note! There are relative and absolute contraindications. For some conditions and diseases (pregnancy, sore throat, pneumonia, relapse of allergies), even a minimal dose of the irritant cannot be administered, but after recovery or the birth of a baby, studies are allowed. In case of absolute contraindications, other diagnostic methods are used, for example, a safe, highly informative blood test for antibodies (food allergen panel).

Types of testing

To identify allergens, doctors conduct several types of testing:

scarification tests. The doctor applies irritant particles to the forearm and makes small scratches with a needle or lancet;
application tests. The safe method does not require even minimal damage to the epidermis: the doctor applies a tampon moistened with an allergen solution to the body;
prick tests. The healthcare worker applies a drop of irritant to the skin, then uses a special needle to carefully pierce the testing area.

What are direct and indirect samples?

Allergists conduct certain types of studies involving the upper layer of the epidermis in the process. The methods are effective in diagnosing allergic diseases, clarifying the diagnosis or type of irritant.

Features of skin tests:

direct allergy tests. The examination is carried out to diagnose diseases that develop due to intolerance to certain substances. During direct tests, the possible allergen and the epidermis are in close contact: applications, scarification tests, and prick tests are carried out;
indirect skin tests. The technique was developed to determine the type of allergic reaction. First, the suspected irritant is administered subcutaneously; after a certain period, the doctor prescribes a venous blood sample to determine the level of antibodies;
provocative tests. The technology is used only when other methods have low information content or false positive/false negative test results. The method allows you to clarify the diagnosis if the data from previous tests and anamnesis do not match. The Prausnitz-Küstren reaction is the injection of blood serum from an allergic person to a healthy person. A day later, the doctor determines the level of antibodies in the epidermis, then the same area is treated with an allergen and the reaction is observed.

Preparation for the procedure

discontinuation of glucocorticosteroids and antihistamines 14 days before testing;
compliance with previously assigned. Test results performed on an empty stomach may be incorrect.

The patient must strictly follow the rules determined by the doctor. False-positive and false-negative results of skin tests are possible if the recommendations are not followed. If the picture is “blurred”, you will have to repeat the study again, using microdoses of allergens, which creates some discomfort for the patient. To clarify the diagnosis, additional medications are prescribed, many of which are not cheap.

How is allergen testing performed?

Features of the scarification test:

before scratching, the epidermis is wiped with 70% alcohol;
testing in children is carried out in the upper back, in adults - in the forearm area;
on the treated area of the epidermis, the doctor makes small scratches, the distance between them is from 4 to 5 cm. If the procedure is carried out incorrectly (the marks are too close), inaccurate results are often obtained);
Using a sterile needle or lancet, the doctor applies extracts or solutions of allergens. For each type of stimulus, the specialist takes a new tool;
for 15 minutes the patient must hold his hand motionless so that the drops of irritants do not mix, the result is reliable;
Based on the reaction on the surface of the epidermis in the scratch area, the doctor concludes whether this substance is dangerous for a particular person or not. Papules, redness, itching, swelling in a certain area indicate a negative response to this component;
The test result is noticeable after a quarter of an hour. After taking measurements and analyzing the situation, the doctor removes the remaining drops of irritant from the scratches. A maximum of twenty allergens can be applied in one procedure.

A prerequisite for correct diagnosis and the absence of complications after the procedure is highly qualified medical personnel. Doctors and nurses must have diplomas and certificates confirming the right to conduct special research. Experience is an important point that you should pay attention to when choosing a medical institution: the body of some patients reacts violently to the management of allergens, anaphylactic reactions develop, and prompt and competent medical assistance is required to prevent serious consequences.

Diagnostic results

Skin tests are a highly informative method that allows you to determine the degree of danger of a substance for a particular patient:

sharply positive test result- pronounced redness, papule measuring 10 mm or more;
positive reaction- redness is clearly visible, the papule reaches 5 mm;
weakly positive result- severe hyperemia, papule no more than 3 mm in size;
dubious outcome- there is no papule, but the skin is red. To clarify the diagnosis, a blood test is prescribed for comparison with a panel of allergens or another type of study at the discretion of the doctor;
negative result- there are no skin reactions on the surface of the epidermis in the scratch area.

False results: reasons

Doctors identify several factors against which inaccurate data is possible:

taking or taking other medications that inhibit the development of an allergic reaction;
incorrect procedure;
decreased skin reaction in a particular patient during a certain period, more often in children and the elderly;
storage of allergen extracts in violation of instructions, which leads to changes in properties;
testing for a substance that is not the main irritant;
The concentration of the solution prepared by the nurse is too low.

For this reason, personnel must quickly respond to acute symptoms and competently stop signs of life-threatening manifestations. With timely desensitization of the body, negative symptoms decrease after a certain time. The period of disappearance of pronounced swelling, normalization of pressure, elimination of blisters depends on the severity of the case.

Skin tests using extracts and solutions of irritants can determine in 15-20 minutes whether a particular substance is an allergen or not. The technique is quite safe, the procedure is simple, discomfort is minimal, and complications occur in rare cases. An important condition is that skin testing be carried out by competent personnel in a medical institution.

How are skin tests performed and what do they show to determine the allergen? Find out more after watching the following video:

Allergen skin testing is a diagnostic method for identifying the presence of increased susceptibility to possible allergens by assessing the strength and nature of the skin's response.

Allergies are caused by many substances and associated factors:

mold,
Food,
pollen,
Poplar fluff,
cosmetical tools,

At the same time, the symptoms for various allergens are almost the same, which does not allow identifying a specific irritant based on examination and questioning of the patient.

Sometimes the immune system of the same person reacts to several pathogens at once, which further complicates the diagnosis. Therefore, skin tests for allergens are prescribed everywhere for the following symptoms:

dermatitis, rashes, urticaria, redness, eczema;
itching of the skin, mucous membranes;
“hay fever”, rhinitis, sneezing, runny nose, nasal congestion;
conjunctivitis of allergic origin;
Quincke's edema;
headache, dizziness, nervous system disorders;
problems with the gastrointestinal tract and other organs and systems against the background of other signs of allergy.

Many people do not know how to take skin tests for allergens, whether this diagnostic method can be used for children, or approximately how much it will cost, so they are afraid to do it.

Allergy sufferers also doubt how reliable skin tests are and whether they will cause pain and worsen their condition. The following information is intended to clarify these controversial points.

Why take it?

A test for possible irritants is necessary in order to confirm or, conversely, refute a preliminary diagnosis, as well as to clarify the suspected allergen, identify allergy triggers that the patient did not know were present, exclude pseudo-allergies, identify other disorders accompanying allergies (lack of enzymes), determine the most optimal treatment method, prescribe effective and safe medications.

Of course, tests do not give an absolutely accurate result, so it is advisable to also donate blood for testing.

Skin testing for allergens is contraindicated under the following conditions:

weakening of the immune system,
exacerbation of allergies,
chronic diseases,
acute infections,
inflammation (for example, ARVI),
long-term use of corticosteroids,
pregnancy, feeding, first days of menstruation,
age over 60 and under 3 years.

The analysis is carried out exclusively during the period of remission. Usually no earlier than a month after the acute stage of the allergy.

Types of tests

There are different types of skin tests.

Scarification: a drop of allergens is applied to the marked (numbered) skin of the forearm. With a special tool, a scarifier, scratches are made directly through droplets of liquid.
Prick tests, which involve puncturing the skin with needles.
Applications made from cotton swabs soaked in a solution with an allergen.
Subcutaneous injections.
Provocative tests - prescribed when symptoms and results of skin tests vary. They are carried out by direct application of the allergen to the mucous membrane of the eyes, nose, and also through inhalation.

In one test you can check no more than 15-20 allergens.

Provocative tests are not included in the number of skin tests for allergens in children. Children under 3 years of age are not given any skin tests, since the child’s reaction to a stimulus changes with age and sometimes disappears altogether.

Older children can take the same tests as adults.

How to take it

The methodology for testing for allergens varies depending on the type of skin test chosen. For example, scarification, prick test performed on previously cleaned forearms. Punctures and scratches are needed to ensure the penetration of the allergen into the inner layers of the epidermis (reliability - up to 85%).

A subcutaneous injection involves injecting a solution with an allergen directly under the epidermis. Applications are made not on the forearm, but on the back. This method does not require any trauma to the skin. For applications, use the most concentrated allergen solution.

A provocative test involves contact of the conjunctiva and nasopharyngeal mucosa with an allergen.

How to prepare

Inform your doctor about any alarming symptoms, pregnancy, or medications you are taking the day before the test. 2 weeks before the procedure, stop taking antihistamines and other anti-allergy medications (stop using ointments a week before).

The skin of the forearms must be disinfected with alcohol before testing.

Evaluation of results

If pronounced redness, swelling, and itching appear at the site of skin contact with the suspected allergen, the reaction can be considered positive. The reaction can appear almost immediately (in half an hour), or in a day or two. It comes in varying degrees of intensity.

In the absence of any symptoms, the reaction is considered negative. If the result of skin tests is weak, they speak of a weakly positive reaction, and if it does not coincide with the symptoms, the result is considered doubtful.

The result can be confirmed using provocative tests and blood serum testing. The presence of antibodies in the blood serum, redness, itching of the conjunctiva, rhinitis, and sneezing after a nasal provocation test are indicators that the test gave a positive result.

Errors are possible if the rules for preparing for the test are violated. To eliminate possible errors, the doctor can apply a couple of drops of dissolved histamine to the skin and a drop of allergen before the test for control. If the skin responds to histamine with redness and itching, but does not respond to the control solution, then an error is excluded.

However, for one in 10 allergy sufferers, skin test results are inaccurate.

Price

Prices for skin tests for allergens vary depending on how many suspected pathogens will be tested, how the allergen will come into contact with the body, and how much the test material itself costs. The prestige of the clinic also matters. Thus, the cost of a skin test in a public and private clinic can differ greatly.

For a minimal price (from 80 rubles) you can be tested for 1 allergen; a test for a group of similar allergens that have the same effect on the human body will be slightly more expensive. The highest cost for one component can be 600-800 rubles.

If the differential diagnosis does not give the desired result, additional skin tests may be required. The most comprehensive picture from tests sometimes costs several thousand (up to 20 thousand rubles or even more).

Expect that you will also have to spend money on a blood test for antibodies (another 300 rubles minimum). The maximum price for a blood test is 4 thousand rubles. and more.

Before taking allergy tests, find out how much they cost in different immunological centers, laboratories, skin clinics at public and private clinics. Remember that provocative tests can only be performed in hospital laboratories, as emergency care may be required.