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Allergy diagnostic tests are one of the easiest and most affordable ways to detect/monitor allergies. Samples are a liquid composition containing a small amount of an allergen that is potentially harmful to humans. It can be pollen, extracts from food or plants. Based on the reaction of the dermis to the allergen, a therapeutic course is developed, the patient’s diet or lifestyle is adjusted. What you need to know about allergy tests, how is the diagnosis carried out and which allergens are allowed to be used in medical practice?
General characteristics of the procedure
According to WHO statistics, allergies are one of the most common diseases on the planet. Every fifth inhabitant of America, every fourth German and every third Russian become victims of this disease. Allergies can be both congenital and acquired and periodically worsen at certain times of the year or with internal changes (for example, a decrease in immunity). To find the cause and methods of correcting the disease, a comprehensive medical examination is carried out. Its most important part is allergic diagnostic tests.
Allergy tests help identify specific antigens that provoke a reaction. There are two main diagnostic methods – skin tests (“in vivo”) and blood tests (“in vitro”). Additionally, elimination and provocative tests are isolated, but they are more specific.
APD is prescribed for any systemic changes in the body – from food allergies to bronchial asthma with allergic etiology. Usually the patient receives the test results on the same day or 3-4 days after the manipulation. Based on the analyzes, the doctor develops a therapeutic course to suppress pathogenic substances, relieving the patient of discomfort.
Where can I take allergy tests?
You should visit your GP before starting APD. He will analyze the patient’s condition, prescribe a list of tests and, if necessary, issue a referral for the study of allergic tests. In addition to the therapist, allergists and dermatologists do this. Additionally, the patient can apply to a private medical diagnostic center.
APD is carried out in immunology centers or skin dispensaries. Some types of diagnostics (for example, provocative tests) are allowed to be done only in hospitals. This is justified by the high risk to the health of the patient. The study is carried out under the strict supervision of specialists who, if necessary, will be able to provide first aid.
The result of standard allergy tests is issued on the day they are carried out. The patient will be able to receive information about the blood test only after 1-3 days (depending on the medical institution).
Preparing for the procedure
If you have doubts about the correctness of the APD results, order a second study at a private medical center or commercial laboratory.
Before conducting allergy tests, you must:
- stop using drugs (including antihistamines) 3-4 days before diagnosis;
- refuse to drink alcohol 2-3 days before the date of delivery;
- stop contact with domestic or outdoor animals (from cats and dogs to reptiles);
- avoid excessive physical activity so that the condition of the body does not affect the results;
- visit a doctor first, if a sharp decline in health is recorded before the diagnosis, report any cold symptoms to your doctor.
Analyzes are taken in the morning on an empty stomach. Children are allowed to be diagnosed 3 hours after the last meal. Allergic tests of babies are no different from a similar diagnosis of adult patients. All age groups should be monitored by a doctor in order to track the reaction in time, prevent side effects and ensure maximum safety.
Babies under 3 years of age are only given a blood test. If an allergic reaction manifests itself in an infant, then the need for blood diagnostics disappears.
In the blood of the baby there are maternal antibodies that enter the body with milk. The doctor decides on the safest and most informative examination method.
Indications and contraindications for APD
The main indication for APD is a suspicion of allergy or an assessment of the risks of allergic pathologies in an appropriate history (for example, in patients with genetic diseases). Allergic diagnostic tests (except for a blood test) are not performed in such cases:
- exacerbation of any chronic pathology;
- decompensated stage of asthma;
- acute stage of the infectious process;
- autoimmune diseases;
- increased risk of developing anaphylactic reactions;
- mental disorders;
- pregnancy / lactation;
- age up to 3 years;
- the first days of the menstrual cycle (the state of the hormonal background may affect the accuracy of the results).
Varieties of diagnostics
Diagnostic tests reveal allergic diseases and pathologies with an allergic component in pathogenesis. They are based on the general / local reaction of a living organism to the introduction of a particular allergen. There are several types of samples, the use of which varies from the individual characteristics of the patient and the specifics of the disease. Among them are skin tests, elimination, provocative ADP, blood tests.
Skin tests
Skin tests are considered the most accessible and safest diagnostic option. There are several methods of introducing the allergen – intradermal, scarification, application. With increased sensitivity to fungal or bacterial allergens, doctors use intradermal tests. They are prescribed to patients who suffer from bronchial asthma, chronic recurrent urticaria, and infectious pathologies.
The sensitivity of intradermal tests is 100 times higher than other types of ADP. However, they are less specific and fraught with serious side effects. Prick tests are suitable for patients with hypersensitivity to pollen/epidermal/household allergens. It is prescribed to patients with bronchial asthma, urticaria, Quincke’s edema, hay fever. Application tests are used when the patient is hypersensitive to simple chemical and medicinal substances. This type of diagnosis is suitable for patients with contact dermatitis.
Some allergens can cause a range of side effects ranging from shock to death. To protect the patient as much as possible, the Praustnitz-Küstner reaction is used. Allergic serum is administered intradermally to a healthy volunteer. It could be a family member or a complete stranger. A day later, the doctor introduces the allergen and observes the skin reaction. After a few minutes, a blood-filled blister forms on the skin, on the basis of which a diagnosis is made.
Some varieties of ADP are used for infectious or parasitic pathologies. The only condition is that the disease must proceed with severe allergic manifestations. For example, for the diagnosis of tuberculosis, an intradermal Mantoux test and a Pirquet scarification test are used, for brucellosis, an intradermal Burne test, echinococcosis, an intradermal Kasoni test, and dysentery, a Tsuverkalov test. If the reaction is positive, then inflammation with hyperemia and swelling will form at the injection site of the allergen.
Some tests are necessary to identify a predisposition to a particular disease. For example, Schick’s reaction when diagnosing diphtheria or Dick’s reaction when determining the risk of developing scarlet fever.
Provocative tests
They are used to confirm or refute the diagnosis after skin tests. There are situations when the result of ADP does not correspond to the medical history and puts doctors in a stupor. To finally resolve the issue, additional research is carried out.
There are several types of provocative tests, among them – a nasal test. It is necessary for the diagnosis of allergic rhinitis.
The patient is given a few drops of control fluid in both nostrils. A person may experience worsening nasal breathing, sneezing, discomfort, or a slight tingling in the nasal passages. These symptoms indicate a positive test reaction. If the reaction does not occur, the doctor increases the dose and observes the patient’s reactions.
The conjunctival test is used to diagnose hay fever and conjunctivitis. First, the doctor manipulates the control substance and only after a preliminary test proceeds to the allergen. It is instilled into the patient’s conjunctival sac (lower eyelid area) and waiting for a reaction. Itching, tearing, or redness indicates a positive test result.
Another type of provocative test is the inhalation test. It is necessary to confirm bronchial asthma. The allergen solution is sprayed with an aerosol. If the test is positive, then the vital capacity of the lungs decreases sharply, which entails bronchospasm. Doctors should immediately stop it with special medicines.
Provocative tests are also used to diagnose physical allergies. For example, a cold test helps to identify chronic urticaria. To do this, a piece of ice is attached to the body for 10 minutes. With a positive reaction on the dermis, a blister develops.
Elimination samples
This is the simplest, but lengthy diagnostic method that is used for food allergies. It is enough for the patient to exclude the alleged allergen from food for a while. Most often, the method is used in infancy, if parents cannot identify the cause of an allergic reaction in a baby.
The time frame for elimination trials varies from 7 to 12 days for 1 food product. At the time of diagnosis, you should keep a food diary, note the general state of health, the body’s reaction to a change in diet.
Blood test (determination of immunoglobulin IgE)
A living organism produces special protein molecules in response to the intake of an allergen. These protein molecules are called antibodies or immunoglobulins E (IgE). The immune system produces antibodies to identify and destroy the pathogenic stimulus. It may seem that the body is equipped with an ideal defense system, but it is not. In the battle with the allergen, protein molecules destroy the cells of their own body, which causes an allergic reaction.
For each allergen, there is a specific type of immunoglobulin E. A blood test determines the concentration / type of IgE, indicating a specific antigen.
How is a blood test done? Venous blood is centrifuged, the necessary allergen or a combination of them is added to the resulting serum. A provocateur and a suitable antibody form immune complexes that are detected using special diagnostic kits. After the study, the patient is given an individual list of potentially dangerous allergens.
As a preventive measure, the patient may take a test to determine the total level of antibodies. This diagnostic is focused on a quantitative, not a qualitative indicator. The concentration of immunoglobulin in the patient’s blood is determined and the results obtained are compared with the norm (varies depending on age). Exceeding the norm indicates the presence of a strong internal allergen, which requires additional diagnosis and treatment.
The test to determine the total level of antibodies is suitable for babies under 3 years old, patients with exacerbation of any chronic pathologies and people who take antihistamines.
Possible complications
Complications may vary depending on the individual indicators of the body and the type of diagnosis. Skin testing is considered the simplest, most economical and acceptable method for detecting individual hypersensitivity. However, they are not without side effects. Delayed-type hypersensitivity (DTH) may develop 6 hours after allergen injection. The total duration of the state reaches from 6 to 24 hours.
Hypersensitivity is an increased sensitivity of the body to a particular substance. The condition is categorized as unnecessarily unwanted because hypersensitivity has a serious effect on immunity. This phenomenon provokes long-term tissue damage at the site of allergen injection. Additionally, there may be a general sensitivity of the body or the formation of a new allergy.
Negative reactions can develop both from medical errors (ignoring asepsis), and from a specific reaction of the body. Even the smallest dose of an allergen can cause angioedema or anaphylactic shock. To protect the patient, the diagnosis is carried out under the supervision of medical personnel.
Angioedema or Quincke’s edema – an increase (swelling) of the face, part of it or limbs. Anaphylactic shock is an immediate allergic reaction. The human body becomes as sensitive as possible when the allergen is re-introduced. In 10-20% of cases, it ends in death.
In general, ADP is considered a safe procedure. Her technique is simple and clear, and complications occur in rare cases. The main thing is to choose a specialized center for testing and strictly follow the doctor’s recommendations. Regularly monitor the condition of the body and be healthy!