Allergy test

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Allergy tests serve to detect allergies to tested allergens from which the person or animal being examined suffers. The following different procedures are used:

In vitro test method

Determination of antibodies

So-called free IgE antibodies can be measured in blood samples . On the one hand, the total IgE level can be measured, which includes all free IgE antibodies. This value enables a statement to be made as to whether more IgE antibodies are generally formed. Elevated total IgE values ​​do not only occur in allergic diseases, but also in parasitic infestation and certain haematological diseases . On the other hand, allergen-specific IgE antibodies can also be detected. The IgE levels that are specifically directed against an allergen source are determined here.

Common today are FEIA (fluorescence enzyme immunoassay) and EIA (enzyme immunoassay) determinations that use instead of the previously used radioactive (125I) labeled reagents, enzyme-labeled reagents. A reference range of <100 kU / L for total IgE applies to healthy people. Measurements for allergen-specific IgE are considered negative for values ​​<0.35 kUA / L. Class 1 (0.35-0.70 kUA / L) is considered borderline positive. Classes 2–6 (class 2: 0.70–3.5 kUA / L; class 3: 3.5–17.5 kUA / L, class 4: 17.5–50 kUA / L; class 5) are positive : 50–100 kUA / L; class 6> 100 kUA / L). RIST (Radio-Immuno-Sorbent-Test) for total IgE and RAST (Radio-Allergo-Sorbent-Test) for allergen-specific IgE are rather outdated measuring methods .

However, the quantitative measurement of IgE antibodies in the blood correlates only poorly with the clinical picture; the measurement of IgE antibodies in the blood allows a statement about the sensitization of an allergic person, but only a limited assessment of the severity of the symptoms and no statement about it the nature of the symptoms. It is also possible that allergen-specific IgE antibodies cannot be detected despite sensitization.

There are now some providers on the market who not only identify the source of the allergen, but also many of the allergen components relevant for sensitization. Since these tests do not measure the antibodies against the allergens , but analyze individual proteins of the allergens, the test is more informative than the aforementioned test methods. Various technologies enable the analysis of specific antibodies against allergens in a single batch (single plex / single parameter test). In another test format, the multiparameter test, however, many different allergen-specific antibodies are determined simultaneously. Allergy screening using a multiparameter test is currently not a service provided by statutory health insurance . The advantage of this collective examination is that an extremely wide range of allergens can be examined with relatively little use of blood. This is particularly beneficial for young children and a complicated medical history . However, allergens or allergen components are also examined that have no anamnestic influence on the clinical picture.

Determination of markers of inflammation

histamine

Main article: Histamine

Tryptase

Leukotrienes

Main article: Leukotrienes

Eosinophilic Cationic Protein (ECP)

  • The eosinophil cationic protein (ECP) is selectively synthesized in eosinophilic granulocytes . Along with EDN, it is one of the main components of the eosinophilic granules. Both proteins are ribonucleases of the RNase A superfamily . The eosinophilic granulocytes play an important role in the pathogenesis of bronchial asthma. There is a close correlation between the number of eosinophils and the ECP concentration. Since there is also a correlation between the ECP concentration in the blood and the extent of the severity of the asthma, this parameter can e.g. B. contribute to monitoring the progress of asthma therapy.

Main article: Eosinophilic cationic protein

Cellular tests

The lymphocyte transformation test (LTT) is a laboratory procedure for the detection of antigen-specific T lymphocytes . It is used in immune function diagnostics in medicine . For a few years it has also been used in allergology to detect certain allergic reactions of the delayed type (IV) (e.g. drug allergy, metal allergy) and in pathogen diagnostics (e.g. Borreliosis diagnostics ).

Several university clinics and specialized institutes have standardized the procedure. For drug allergy, the test was included in the recommendations of the German Society for Immunology and Allergology (DGAI) in 2006. In the case of other allergological questions, however, the clinical significance of a proven sensitization is still controversially discussed. For this reason, the LTT should only be used in addition to the patch test for allergological issues or if this cannot be carried out.

Main article: Lymphocyte transformation test

Skin tests

Prick test

The prick test is usually carried out on the forearm

The skin prick test (English: prick = puncture) is used to detect a so-called type I allergy , such as a sensitization against pollen or animal hair. Here, a defined allergen extract is dripped onto the skin and then gently pierced with a lancet so that the respective substance can penetrate the epidermis. The test reaction can be read off after 20 minutes in comparison to two blank tests that were always carried out ( positive control with histamine and negative control free of active substances ). The reddening of the skin and the size of the wheals are assessed. The prick test is usually painless.

A sub-form of prick testing is the so-called prick-to-prick test, in which, for example, food can be tested by first piercing the food and then the skin.

Intracutaneous test

Here, a defined amount of an allergen extract (e.g. insect venom or food extracts ) is injected intracutaneously and also read off after 20 minutes against an empty test (see above). However, there is a risk of a severe allergic reaction. It is also used to detect a type I allergy.

Rub test

Allergy test, which is also suitable for the detection of type I allergies, in which the skin is first scratched on the surface and then the allergen to be tested (e.g. animal hair or food) is rubbed in natively. The test reading also takes place after 20 minutes.

Patch test

This test is used to prove a sensitization to a so-called type IV allergy , such as to nickel salts (nickel sulfate) or fragrances . Defined preparations of the allergens in carrier substances (such as petroleum jelly or water) are glued to the skin under test chambers. The test reading should take place after 24, 48 and 72 hours (in exceptional cases even longer). The course of the reaction (rising or falling reaction) is also assessed over time.

ROAT

The repeated open application test is used to clarify an unclear or ambiguous reaction to the patch test. To assess the clinical relevance, the allergen in question is applied to a delimited area on the inside of the upper arm twice a day for one week.

Atopy patch test

This special form of the patch test is used to identify type I allergens (inhalation allergens) as triggers of atopic eczema . Vaseline is used as a carrier substance. The test area should be symptom-free at the start of the test. A positive test reaction is a disruption of the skin's barrier function, which leads to eczema.

Provocation tests

Nasal provocation testing

The allergic rhinoconjunctivitis (allergic rhinitis, hay fever) is the most common allergic diseases. It often begins in childhood, often leads to annoying symptoms over decades and has an impact on social life, school performance and the productivity of the patient. It is clinically defined as a symptomatic hypersensitivity reaction of the nose , induced by IgE-mediated inflammation of the nasal mucosa as a result of allergen exposure.

A positive result of mastzellgebundenem allergen-specific IgE in the skin test or by specific IgE in the serum is an immune response to an allergen, but is not equivalent to the detection of an allergic disease. The aim of the nasal provocation test with allergens is to separate patients with a clinically current sensitization (allergy) to inhalative allergens from those patients who, although sensitized, show no symptoms under natural exposure conditions (clinically silent sensitization), of diagnostic importance especially in the case of of rhinitis .

The nasal provocation test (NPT) reproduces the reaction of the nasal mucosa to an inhalable substance from the environment under controlled conditions. The suspected allergen is applied to the nasal mucosa and the resulting immediate clinical reaction is documented. The change in nasal air permeability after allergen application is measured by means of active anterior rhinomanometry , sneezing, secretion and remote symptoms are recorded by means of a score.

Pulmonary function diagnostics

Peak flow measurement

The peak flow is indicative of the speed with which a person air from its one reading lungs can blow. This is measured with a peak flow meter or a spirometer . In healthy people, the peak flow value is between 400 and 700 l / min. For people with breathing difficulties, such as bronchial asthma , the value is lower. In asthma sufferers, the airways are narrowed, which means that the amount of air blown out per minute is significantly lower. For this reason, peak flow in patients with respiratory diseases is considered to be as important as daily blood pressure measurements in patients with high blood pressure.

Bronchospasmolysis test

When bronchospasmolysis the reversibility of bronchial obstruction is tested. For this purpose, it is investigated whether a reduction in the airway resistance can be achieved in the patient by using a β 2 sympathomimetic (for example: terbutaline , fenoterol or salbutamol ). This is accompanied by an increase in the one-second capacity (FEV 1 ). Typically, the obstruction in bronchial asthma is reversible, while the obstruction in chronic obstructive bronchitis is never completely reversible.

Inhalative provocations

Nonspecific inhalative provocation

Nonspecific inhalative provocations are studies with pharmacological substances that have bronchoconstrictive effects. The examination is indicated in patients with chronic cough and / or shortness of breath of unknown origin, if there is no spontaneous measurable obstruction. The methacholine test with the cholinergic methacholine is predominantly used today to carry out this . Compared to other substances such as histamine or carbachol , undesirable local or systemic side effects or delayed effects are not to be expected.

Main article: Methacholine test

Specific inhalation provocation

Specific inhalative provocations are used to detect a specific allergen as the trigger for allergic bronchial asthma . Possible indications are also in the area of occupational medical reports (for example baker's asthma) or for definitive proof of the triggering allergen, for example if there are serious therapeutic avoidance measures or social consequences (change of occupation). Another indication for specific provocations are insect bites, in which the success of the therapy can be checked in individual cases with a desensitization in case of insect venom allergies .

Provocations with food and additives

See also

Individual evidence

  1. Allergy screening at tk.de.
  2. ^ Insect venom allergy - guideline of the German Society for Allergology and Clinical Immunology (DGAI) . (PDF; 129 kB) In: Allergo J. 13, 2004, pp. 186–190.
  3. P. Altmeyer: Encyclopedia of Dermatology, Venereology, Allergology, Environmental Medicine . 2002, ISBN 3-540-41361-8 ( online [accessed March 4, 2008] entry Repeated open application test ).
  4. P. Altmeyer: Encyclopedia of Dermatology, Venereology, Allergology, Environmental Medicine . 2002, ISBN 3-540-41361-8 ( online [accessed March 4, 2008] entry Atopie-Patch-Test ).
  5. Allergic rhinoconjunctivitis - guidelines of the German Society for Allergology and Clinical Immunology ( Memento of October 24, 2004 in the Internet Archive ) In: Allergologie. 26 (4), 2003, pp. 147-162.
  6. Validity of body plethysmography and spirometry for recording bronchial hyperreactivity with methacholine. (PDF; 102 kB) Trade Association Research Institute for Occupational Medicine (BGFA), Bochum.
  7. German Society for Allergology and Clinical Immunology: Guideline for the implementation of bronchial provocation tests with allergens.  ( Page no longer available , search in web archivesInfo: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice. (PDF; 124 kB).@1@ 2Template: Dead Link / www.pneumologie.de  
  8. Diagnostic procedure when a pseudo-allergic reaction is suspected due to food ingredients - guidelines of the German Society for Allergology and Clinical Immunology. (PDF; 407 kB) In: Allergology. 23, 2000, pp. 572-579.

Web links

Wiktionary: Allergy test  - explanations of meanings, word origins, synonyms, translations

literature

  • Peter Angerer: Allergology Handbook: Basics and Clinical Practice . Schattauer, Stuttgart / New York 2006, ISBN 3-7945-1972-8 .