Skin Allergy Tests

General Description

Skin allergy tests are a method used to identify the specific substances, or allergens, to which a patient is allergic. Common allergens include pollen, dust mites, animal dander, metals, insect stings, certain foods, and specific medications.

The principle of skin allergy testing is to expose the patient’s skin to a controlled dose of possible allergenic substances and observe whether an allergic reaction occurs.

When Are They Indicated?

Skin allergy tests are performed when a patient presents symptoms consistent with an allergic reaction, especially if they are persistent or severe. These symptoms vary depending on the specific allergen, with the most common being:

Respiratory Symptoms:

• Nasal congestion and discharge.
• Itching in the nose or throat.
• Watery eyes.
• Coughing, sneezing.
• Difficulty breathing, wheezing.

Skin Symptoms:

• Itching and dryness of the skin.
• Rash, eczema, blisters.

Digestive Symptoms:

• Abdominal pain, gas, diarrhea.

Ocular Symptoms:

• Itching.
• Swelling.
• Redness.
• Watery eyes.

Anaphylaxis:

An extreme allergic reaction that affects the cardiovascular system and can lead to airway obstruction. It can be life-threatening.

How Are They Performed?

To expose the skin to potential allergens, allergenic extracts are used. These are solutions obtained by fragmenting, dissolving, filtering, and sterilizing natural allergens to create an aqueous solution rich in allergenic proteins. Typically, extracts related to the patient’s symptoms and commonly found in their environment are used.

Skin tests are usually performed on the arm (in children, they may be done on the back). There are two different techniques:

Prick Test (Prick-Test):

Drops of various allergenic extracts are placed on the skin in a controlled order, with a few centimeters of separation between them. A needle or lancet is then used to puncture the skin, allowing the extract to penetrate the superficial layer. The allergen remains on the skin for 15 to 20 minutes, after which the skin is examined for signs of an allergic reaction (rash and redness). Additionally, control substances are tested to verify the reliability of the results:

• Histamine: This substance usually causes an allergic reaction in most people. If no reaction occurs, the patient may have a false negative result, meaning they could still be allergic to other substances despite a lack of reaction.
• Saline solution or glycerin: These substances generally do not cause any reaction. If the skin reacts, it may indicate sensitive skin, which means the patient could react to allergenic extracts without actually having an allergy (false positive).

A variant of the prick test, called the prick-prick test, is mainly used to detect food allergies. This involves inserting the needle into a fresh food sample and then pricking the skin. This method provides greater sensitivity than using extracts.

Intradermal Test:

The procedure is similar to the prick test, but in this case, the allergenic extract is injected directly into the skin. It is mainly used to verify allergies to insect venom or penicillin. It is also performed when the prick test results are inconclusive.

Risks

Skin allergy tests have a very low risk percentage. However, in highly allergic patients, particularly those allergic to medications, there is a possibility of triggering a severe anaphylactic reaction, though this is uncommon. If the patient has a history of anaphylaxis, a blood allergy test may be recommended instead of a skin test.

What to Expect from a Skin Allergy Test

Before the procedure begins, the arm area where the test will be performed is disinfected, and the exact spots for applying the different allergenic extracts are marked. Mild discomfort may be felt during pricks or injections, but the procedure is generally not painful.

The test takes approximately 20 to 40 minutes, depending on the number of allergens being evaluated. Once the results are reviewed, the marks are cleaned, and the patient can resume their normal routine. If an allergic reaction occurs, symptoms may persist for a few days.

Medical Specialties That Request Skin Allergy Tests

Skin allergy tests are requested by the allergology department.