The prick test is an internationally recognized standard procedure for detecting type 1 allergies (immediate reaction) such as pollen or food allergies. In all cases, a prick test is associated with only minor risks and side effects.
What is the prick test?
The prick test is an internationally recognized standard procedure for detecting type 1 allergies (immediate reaction) such as pollen or food allergies. The prick test is an allergological examination procedure that, analogous to the scratch test, can be used to identify the allergens (allergy-causing substances) that trigger a type 1 allergy (antibody-mediated allergic reaction of the immediate type). Food allergies, allergic asthma or hay fever are characteristic allergies that can be detected in a prick test. For this purpose, different test solutions containing allergens are applied to marked areas of skin on the forearm or in the upper back region and the skin is pricked superficially with a prick lancet or prick needle. Based on the reactions, the triggering allergen and expression of the specific allergy present can be determined.
Function, effect, and goals
A prick test is generally used to detect or exclude sensitization to specific allergenic substances (allergens). The prick test is particularly suitable for the detection of type 1 allergies. Type 1 allergies are characterized by the fact that the immediate (a few seconds to minutes) allergic reaction is mediated by IgE antibodies (immunoglobulins E). Upon contact with the allergen, the organism forms IgE antibodies that bind to the mastocytes (mast cells) of the immune system and cause a release of inflammatory mediators (inflammatory messengers) such as histamine and leukotrienes. These cause acute inflammatory reactions (including hay fever, allergic asthma, urticaria or hives). A standard test usually comprises about 15 to 20 test solutions with the most common allergens, although these can be individually adapted or expanded (including special foods, pollen types, insect venoms) depending on the specific problem. The allergens to be tested are dripped onto areas of skin marked with a pencil on the inside of the forearm or on the upper back. The skin is then pricked superficially with a prick needle or prick lancet without bleeding so that the allergens to be tested can penetrate the epidermis. If an allergy is present, the release of histamine causes the fine blood vessels to dilate and redden. The blood vessels also become more permeable, so that interstitial fluid (tissue fluid) can escape and the skin swells (wheal formation). The additional nervous irritation can also cause pruritus (itching). The evaluation or assessment of the test result usually takes place after about 15 to 20 minutes and is compared with a positive control (0.1 percent histamine solution) and a negative control with saline solution for a better assessment. In the negative control with sodium chloride, no wheal formation should manifest, whereas in the positive control this should occur due to the histamine applied. On the basis of the diameter of the redness and wheals present and the corresponding symptoms, the severity of the allergy can be determined. Finally, the results are recorded in a test protocol or allergy passport. A specific form of the prick test is the so-called prick-to-prick test, in which the prick lancet is first pricked into the test solution and only then into the marked skin area.
Risks and side effects
In general, a prick test correlates with few side effects and risks, although in rare cases pronounced local reactions may be induced. In very rare cases, generalized pruritus, respiratory distress, and/or anaphylactic shock (circulatory collapse) may be observed. The risk of more pronounced reactions is particularly increased when non-standard allergen solutions (including substances brought by the affected person), to which there is a strong sensitization, are tested in the prick procedure. In addition, in some cases the evaluation of a prick test may prove difficult.Thus, the skin reaction does not necessarily reflect the degree of sensitization or allergy in every case. Despite a stronger sensitization, in some cases only a weak reaction can be triggered and vice versa. In particular, applied solutions containing pollen and/or food allergens may contain substances that also have botanically related species, so that a reaction may be observed but the underlying allergen has not been identified. In addition, certain medications such as antihistamines, corticosteroids, sleeping pills, sedatives, and immunosuppressants (drugs that suppress the immune system) may affect the results of the prick test and should be discontinued in advance if necessary. Irritation, inflammation, and damage to the test area should also be ruled out in advance of the prick test, as these can lead to an increased reaction and correspondingly to positively incorrect results.