Allergy Skin Testing
What is Allergy Skin Testing?
Allergy skin testing is a method used to identify substances in an individual that could cause an allergic reaction. The skin test helps to identify which allergy-causing substances to avoid and helps your doctor design a specific treatment plan to treat your allergies.
When the body is attacked by a foreign substance, the immune system produces antibodies to destroy it to protect you from becoming sick. Allergies are responses from your immune system that occur when a foreign body triggers antibody release, even if it is not harmful. These allergy-causing substances are called allergens.
Signs of an allergic reaction include inflammation of the skin, airways, digestive system or sinuses. The severity of allergies can range from minor irritation to a life-threatening emergency called anaphylaxis.
Allergies are specific to each individual. The allergens that affect one person may not cause any reaction in another.
Indications for Allergy Skin Testing
Allergy skin testing is indicated for the following:
- Hay fever or allergic rhinitis (allergic to pollen)
- Asthma (allergic to dust mites and animal dander)
- Food allergies (allergic to foods such as nuts, eggs or sea food)
- Dermatitis or eczema (allergic to dust mites and animal dander)
- Penicillin allergy (allergic to the antibiotic drug penicillin)
- Latex allergy (allergic to natural rubber latex)
- Bee venom allergy (allergic to bee venom)
However, you may be advised against allergy skin testing for the following reasons:
- History of a severe allergic reaction
- Medications you take may interfere with the test
- Large areas of skin affected by skin conditions such as eczema and psoriasis
Procedure of Allergy Skin Testing
There are three types of allergy skin testing that can be performed:
A skin prick test, also called a puncture or scratch test, assesses for immediate reactions to around 40 allergens such as pollen, dust, pet dander, mites and certain foods. Adults are generally tested on the forearm, and children are tested on their upper back.
The test site is cleansed with alcohol and small marks are drawn on your skin. A drop of the allergen extract is placed on each mark and separate lancets are used to prick the allergens into the skin. Along with the allergen extracts, histamine and glycerin or saline are also introduced into the skin as controls. Histamine is the substance that causes a skin response to any foreign body. So, if you don't react to it, none of the other test sites will show a reaction. A reaction to glycerin or saline indicates sensitive skin; the test results will be interpreted cautiously.
During a skin injection test a small amount of allergen extract is injected directly into the skin and examined after about 15 minutes. This test is suggested to test for insect venom or penicillin allergies.
Patch testing is performed for allergic skin irritation. Around 20 to 30 allergen extracts are applied on patches, which are placed on your skin. The patches are worn for about 48 hours, during which time, you are advised not to bathe or participate in activities that could cause excess sweating. The patches are then removed in your doctor’s office and your skin is examined for allergic reactions. The patch test is useful for allergens that cause delayed responses.
After a set period, the test site is observed for a reaction and the size of the swelling is measured.
A positive test is indicated by a raised, red, itchy bump called a wheal at the region where the allergen was introduced. This reaction can show immediately or after several days depending on the allergen. No sign of a reaction shows that you are not allergic to that particular allergen. The size of the wheal indicates how sensitive you are to a particular allergen.
Advantages & Disadvantages
Allergy skin tests are simple and provide fast results. However, they may not always be accurate as they sometimes provide false-positive results, (positive results for an allergen when you are actually not allergic to it) or false-negative results(negative results for an allergen you are allergic to.)
Risks and Complications
The most common risk associated with skin testing is developing wheals, raised, itchy, red patches on the skin. Rarely, allergy skin testing may cause an immediate severe allergic reaction called anaphylaxis that requires emergency treatment.