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General Practice 2023

Allergy testing: what é, when to do and how é done

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Allergy testing: what é, when to do and how é done
Allergy testing: what é, when to do and how é done

The allergy test is a type of exam indicated to identify whether the person has any type of skin, respiratory, food or drug allergy, for example, and thus indicate the most appropriate treatment according to the frequency and intensity of symptoms.

The allergy test is usually recommended by the dermatologist or allergist when the person has itching, swelling or redness of the skin, and can be done by applying the potentially allergenic substance to the forearm or back, or by ingesting a particular food, if a food allergy is being investigated.

This exam is performed in the doctor's office and it is recommended to avoid the use of creams before the exam and the use of antihistamine drugs, as they can interfere with the exam result.


When is indicated

The allergy test is indicated by the doctor mainly when the person has signs and symptoms of allergy, such as:

  • Itching;
  • Swelling;
  • Redness on the skin;
  • Swelling in the mouth or eyes;
  • Frequent sneezing;
  • Coryza;
  • Gastrointestinal changes such as diarrhea.

Thus, according to the symptoms presented by the person, the doctor may indicate the most appropriate exam to investigate the cause of the symptoms, which may be the use of some medications, reaction to some product or tissue, mite or dust, latex, mosquito bite or animal hair, for example. In addition, another common cause of allergy and which should be investigated by allergy tests are foods, especially milk and dairy products, eggs and peanuts. Learn more about food allergy.

How to prepare for the test

To perform the allergy test, it is recommended that the person suspend the use of some medications that may interfere with the result, especially antihistamines, because the use of this medication can prevent the body's reaction to the substance being tested, it was not possible to identify the allergy.

It is also recommended to avoid the application of creams, especially when the skin allergy test is indicated, as it may also interfere with the result.

In addition to these guidelines, the patient must comply with all the specific indications that the doctor has indicated, so that the allergy test correctly informs the cause of the allergy.

How it's done

The allergy test may vary according to the signs and symptoms presented by the person and type of allergy to be investigated, and may be recommended by the doctor:

1. Forearm allergy test

The forearm allergy test, also called the Prick test, is done by applying a few drops of substances known to cause allergies to the forearm. In some cases, in addition to applying the substance to the skin, a few pricks with a needle can also be done.

After application, wait 20 minutes to check for a reaction. The reaction is said to be positive when the presence of a red ball at the site is verified, which can cause swelling and intense itching at the site. Understand how the forearm allergy test is performed.

2. Back allergy test

The back allergy test, also known as contact allergy test, consists of sticking an adhesive tape on the patient's back with a small amount of the substance that is believed to cause allergy. Then, wait up to 48 hours and observe if any skin reaction appears.

3. Oral provocation test

The oral provocation test is performed with the objective of identifying food allergy and consists of ingesting a small amount of the food possibly causing the allergy and then observing the development of a reaction.

4. Blood test

In some cases, the doctor may also recommend performing a blood test to identify the presence of substances in the blood that may be indicative of an allergy.

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