Allergic skin tests (allergen skin tests), which include skin prick tests and epidermal patch tests, are intended to confirm the initial diagnosis of the allergist. In addition, they allow you to assess the severity of allergies. The results of skin allergy tests allow you to select the dose of the drug and determine the optimal duration of treatment.

Allergen (allergic) skin testsis the easiest method to find the cause of an allergy. It is better at detecting inhaled allergens, slightly less food and contact allergens.

According to allergists, skin tests are better to be carried out in children who are 3-4 years old - it is easier to cooperate with an older child, and the results are then more reliable.

Skin tests are usually repeated after 2-4 years, especially if you suspect they may sensitize you to new allergens. There are two types of allergy skin tests:skin prick testsandepidermal patch tests .

Skin tests: preparation for the test

Allergenic (allergic) skin tests should be performed when you do not have allergy symptoms. Since some medications may falsify the results of skin tests, they should be discontinued, of course in consultation with a doctor. In places where tests will be performed, ointments containing glucocorticosteroids and calcineurin inhibitors cannot be used. It is also assumed that:

  • 7-14 days before the test, stop taking antihistamines such as hydroxyzine and second-generation drugs containing cetirizine, levocetirizine, loratidine, desloratidine, fexofenadine, bilacstine
  • 5 days before the test, stop taking ketotifen
  • we stop taking drugs containing diphenhydramine and promethazine 1-3 days before the test
  • 5 days before the test, stop taking ketotifen
  • painkillers and glucocorticosteroids should also be discontinued if the daily dose exceeds 10 mg per prednisolone.

Skin tests: test run

Droplets of various suspensions containing sensitizing substances from the allergen screening kit are applied to the forearm or back one by one:

  • early dusting trees: hazel, black alder, white poplar, elm, willow
  • late-pollinating trees: birch, beech, English oak, plane tree,ash, linden
  • pollen of grasses and cereals: meadow fescue, meadow grass, English ryegrass, ryegrass, cocksfoot, woolly spikelet, rye, wheat, oats
  • pollen weeds: mugwort, plantain, goldenrod, nettle
  • mold fungi
  • pet dander: dog, cat, hamster, guinea pig, rabbit
  • house dust mite.

10-20 allergens are checked at a time. Additionally, two so-called checks:

  • positive, which is a histamine solution at a concentration of 1: 1000; it should cause erythema, a histamine bubble (i.e. it will lift the skin slightly) and a slight itching, which is a normal reaction, allowing the assessment of reactions appearing after the application of allergens;
  • negative - saline solution.

The doctor or nurse gently pricks the epidermis with each drop of allergen that is applied. It is a painless procedure, punctures usually do not even bleed. A special disposable lance is used for this, so there is no risk of transmitting infections, eg hepatitis B or HIV. After each puncture, a small amount of the allergen solution is released under the epidermis.

Skin tests: results

If you are allergic to a given allergen, it will trigger an allergic reaction after approx. 15 minutes: redness, bubbles like a mosquito bite and itching. The skin reaction is proportional to the degree of sensitization, i.e. the greater the blister and redness, the more sensitizing the allergen. The allergic reaction is self-limiting after 30-60 minutes. The STP result the patient receives is the diameter of the erythema and the urticarial wheal in millimeters and on a five-point scale, from 0 to 4 pluses:

  • 0 - allergenic reaction equal to the reaction to saline solution
  • + - mean diameter of the allergen bubble greater than the reaction to the negative control fluid, but less than half the mean diameter of the histamine bubble
  • ++ - the average diameter of the allergen bubble greater than half or almost equal to the average diameter of the histamine bubble
  • +++ - the average diameter of the allergen bubble equal to or slightly greater than the average diameter of the histamine bubble
  • ++++ - the average diameter of the allergen bubble at least twice as large as the average diameter of the histamine bubble or any reaction with quasi-legs (i.e. irregular protrusions).

A positive result is three to four plus, and a negative test is zero and one plus. A test with two pluses is considered a questionable result.

Skin testing: epidermal patch testing (NTP)

A kind of testskin is also calledpatch test . It is performed more often in the case of a contact allergy.

The standard set of allergens used for NTP consists of metals (chromium, cob alt, nickel), preservatives, fragrances, drugs (neomycin), and dyes.

Epidermal patch tests are performed on the skin of the back. The doctor soaks a special tissue paper with the allergen (or puts the allergen in the form of a paste into the chamber of a special patch) and sticks it on the skin for 48 hours. Then he checks for the first time to see if there is an inflammatory reaction. Another check takes place 72 hours after the start of the tests.

Epidermal patch test results are positive from 0 to three pluses with at least 2 pluses:

  • 0 - no reaction
  • + - erythema
  • ++ - erythema, papules
  • +++ - erythema, papules, vesicles

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