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Prick test: the allergy skin test identifies sensitivity to food and inhalant allergens

Prick test: the allergy skin test identifies sensitivity to food and inhalant allergens

The allergy skin test is called the Prick Test or puncture test. It is an "in vivo" method that detects which allergens (substances of natural, environmental or food origin that can induce an allergic reaction) that the individual is sensitive. When the clinical history suggests the involvement of an immunological mechanism with the participation of an antibody called IgE (Immunoglobulin E), specific IgE is investigated for a particular allergen.

This test is capable of detecting sensitivity to inhalants as , for example: mites, grasses (pollen), fungi, dog epithelium, cat epithelium, feathers and cockroaches. It can also detect sensitivity to foods such as milk and fractions (alpha-lactoalbumin, beta-lactoglobulin and casein), egg yolk, wheat, corn, peanuts, gluten, cacao, shrimp, fish, beef, pork and meat

The test can be performed at any age, as long as there is strong clinical evidence.

In order to perform the test, it is important that standardized extracts and appropriate punctures are used, in addition to having professionals qualified with material for any emergency. The puncture skin test is an attribute of the allergist specialist and although very safe, it can trigger systemic reactions, which are rare.

How the test is performed

The test is performed on the volar region of the forearm (the part that does not (where there is no papule, circumscribed elevation of the skin, a solid consistency less than one centimeter in diameter and no scar), a drop of positive control (histamine ) and a drop of suspicious extract. A small puncture is made on the skin at the site of the drop representing the suspect extract, and 15 minutes is waiting for the diameter of the papule to be read. This puncture is performed on all suspected allergens at the same time.

The appearance of the papule represents a reaction in which the specific IgE antibody is present against the tested allergen. Positive results are considered to have a papule diameter greater than or equal to 3 millimeters in relation to the negative control. Histamine will always form a papule greater than or equal to three millimeters. The significance of the positive test is related to an awareness and not necessarily an allergy. In order to prove the allergy, there must be a clinical correlation.

In the case of food proof can be obtained with oral provocation test. Negative testing usually indicates that there is no allergy. It may happen that the test remains positive and the patient is already tolerant to a food, for example cow's milk.

There is a variation of the test called "Prick to Prick" where, instead of the use of extracts, the allergen tested is offered in the form "in natura" (for example, fruit in the natural state). Apply the puncher on the fresh fruit or vegetable and then on the skin of the patient's forearm. This test is used to detect sensitization of fruits and vegetables.

The Prick test takes an average of 30 to 40 minutes to complete, with the use of more modern punctures the period may be shorter.

The conditions that make it impossible the test is:

  • Use of antihistamines (must be discontinued 5 days before the test)
  • Use of antidepressants
  • Use of beta-blockers
  • Presence of extensive skin lesions (eg Atopic dermatitis )
  • Dermographism (a type of skin allergy)
  • Coagulation disorders
  • Previous history of anaphylaxis with the allergen tested

It's a fast read test, where the result comes out the same day. Its usefulness is to identify the triggering factor of the allergy, so that it can provide an environmental orientation for the patient, if it is an aeroallergen (ex: dust mites). If it is a food, it is proposed a diet of exclusion. The test is also important for formulating specific immunotherapy for the patient, if that is the therapy chosen.


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