The reaction is due to the release of histamine, a chemical naturally present in the body, which causes swelling, redness and itching (also known as whiplash or urticariform papule). The test is usually performed or supervised by an allergist.
When will the review be undertaken?
It is your doctor who will determine the timing and frequency of this examination.
A skin allergy test is performed to identify which allergen causes allergy symptoms (such as sneezing, nasal congestion, itchy eyes, wheezing, rash and swelling) so that people Allergy sufferers may avoid the triggering factor if necessary and establish appropriate treatment with their physician.
There are many allergens, including foods, medications, environmental substances such as ragweed and fungi, and some contact allergens that irritate the skin.
A skin allergy test is performed when considering antiallergic injections. The test may also be necessary for people who may develop severe allergic reactions or asthma.
Risks and precautionary measures
Although skin allergy tests are generally considered safe, they are in fact associated with certain risks of adverse reactions or complications: among them, we find urticaria or the appearance of edema balls red and itchy on the skin.
Some people have very serious allergic reactions, called anaphylactic reactions. If a person has had an anaphylactic reaction to an allergen in the past, they may not have an allergy skin test because a dangerous reaction may occur.
The most serious risk associated with the sting test is the anaphylactic reaction. This reaction is a medical emergency: it causes breathing difficulties and a serious drop in blood pressure. However, anaphylactic reactions following the sting test are rare and the allergist will monitor you closely.
It is possible that the skin test can not be performed in the presence of certain skin disorders such as severe eczema or atopic dermatitis.
If a symptom worries you as a result of this test, consult your doctor. Take the time to learn about all the risks of complications and side effects as well as the precautions that you or your doctor should take to avoid them. Make sure your doctor understands your concerns.
What’s going to happen ?
There are three different types of skin tests.
The first test is called “scarification test” or “bite test”. A small amount of allergen is inoculated into the skin by means of a puncture or scratch with a sterile needle. If the stung area is red, itchy or swollen, the allergy skin test is positive. If there is no reaction, it is negative. This test is generally used to establish allergies to pollen, mold, pet dander, dust mites and food.
The second test is called “intradermal test”. A small amount of substance is injected into the skin. This test may be performed when the sting test is negative, but there is still a belief that the person is allergic to the substance. This test is generally used to identify an allergy to bee stings and other insect venoms or penicillin.
The third test is called “patch test”. The substance is fixed on a transdermal patch that is applied to the skin for up to 48 days. Another appointment will be scheduled 2 days after removal of the transdermal patch so that the doctor can examine the skin again. This test shows if a person develops a contact dermatitis (rash), allergic reaction on the skin due to direct contact with an allergen, such as latex, drugs or perfumes.
Skin allergy tests are usually performed on the back or the back of the arm, depending on the number of allergens to be tested. If one person is tested for multiple allergens, it is possible to use a grid as a guide to separate and monitor different allergen sites.
A reaction can usually be seen within 15 minutes of scarification and intradermal testing, while patch test results are usually evaluated after 48 hours and again 96 hours later. It is best not to bathe, shower or perspire excessively when wearing the skin patch to prevent it from coming off and falling.
If you have an allergic reaction to any of the skin tests, you may experience itching, tenderness, and swelling in the affected area. These symptoms can be relieved by a cold compress or steroid cream.
Your doctor may choose to have a blood test in addition to the allergy skin test. This analysis measures the level of antibodies in the blood. The level of antibodies can be high if the person is allergic to the substance. A blood test can also be performed when a person can not have an allergy skin test.
Conditions of the exam
Before you take this test, talk to your doctor about the benefits, disadvantages, long-term risks and consequences associated with it. Make sure you understand what is going to happen and get explanations from your doctor that satisfy you.
Before you submit to a skin or blood allergy test, you must not impose any food restriction (liquid or solid food).
Tell your doctor about everything you are taking, whether prescription or over-the-counter medications and herbal remedies. Also tell them about all your drug allergies and any health problems you may have.
Ask your doctor or pharmacist if you need to stop taking any of your medications before the test. Your doctor may ask you to stop taking certain medications before the test. For example, antidepressants or antihistamines can influence the results of the allergy skin test. Antidepressants and antihistamines have no effect on a blood test.
What will I feel after ?
If your allergy skin test is positive, there are several things you can do to prevent the return of an allergic reaction. Some people undergo desensitization, which involves gradually injecting small amounts of allergen into the body, in order to develop immunity to the allergen.
If an allergic reaction occurs, antihistamines can be used to relieve symptoms.
Your allergist may also discuss effective strategies to avoid or minimize your exposure to allergens.
You can read the results of a prick test and a skin test in about 15 minutes. The allergist will be able to give you the results during the same visit. When the patch test is used, you must return to consulting your doctor’s office 2 days (48 hours) and 4 days (96 hours) later. The doctor can then give you the results. Blood samples are sent to a laboratory and it may take a week before results are available.
The accuracy of the skin tests may vary. It is possible that you react differently to the same substance at two different times or that you have a positive result to a substance but that it does not pose a problem in everyday life.