What is a Skin Prick Test?
A skin prick test, also called scratch test, checks for immediate or delayed allergic reactions to different substances called allergen. This test is usually done to identify allergies to foods, mold, pet dander, dust mites and pollen. The skin prick test is widely used and it is the most sensitive indicator of allergen sensitivity carring very low risk of serious side effects to patients.
What is the Principle of the Skin Prick Test?
Skin prick test give information about the presence of specific IgE to allergen. Cells which react to allergens in the body by releasing histamine (Mast cells) can be found in the sub-ephithelial layer on the respiratory tract, GI tract and skin. Small amounts of allergen is introduced into the body through the skin (epidermis and non-vascular superficial dermis) and interact with specific IgE. Histamine and other mediators are released, causing swelling, redness, and itching (“wheal-and-flare” reaction), peaking after about 20 minutes.
How is the Skin Prick Test Performed?
After choosing the site for the test, that usually is the forearm or the back, the site area is cleaned with alcohol and then marked with the name of the allergens. After that a drop of allergen extract is applied on the skin next to each mark. A disposable plastic lancet is used each time to prick the extracts into the skin’s surface and after twenty minutes the wheal and erythema reaction will be analysed and dimensions will be measured. The final result will be given by the doctor.
The type of lancet used barely penetrate the skin’s surface, so the test is not painful. Since the prick is performed under epidermis, the area won’t bleed and the patient will not feel more than a mosquito bite.
How do I prepare for a Skin Prick Test?
- Please avoid certain medications for at least 1 week before the test:
- Cough medicines
- Steroids (also topic lotions)
- Other systemic drugs: biologics and antidepressants (Doxepin, Desipramine).
- Please do not apply any cream, body lotion or perfume the day of the test.
- You can eat your diet as per normal, fasting is not required.
- The test will take around 45 minutes.
List of allergens you can test for:
GRAINS: Barley, Corn, Oat, Rye, Soya, Wheat.
EGGS & FRACTION: Egg White, Egg Yolk.
NUTS: Almond, Cashew, Hazel Nut, Peanut, Walnut.
FISH & SEAFOOD: Cod, Salmon, Tuna, Crab, Lobster, Prawns.
MEATS: Beef, Chicken, Pork.
MILK & DAIRY PRODUCTS: Cow’s Milk, Goat’s Milk.
FRUITS: Apricot, Banana, Mango, Orange, Peach, Strawberry.
VEGETABLES: Garlic, Mushroom, Onion, Tomato.
SPICES: Cacao (Chocolate), Sesame, Black pepper.
OTHERS: Brewer’s yeast.
MOULDS MIX: Aspergilli mix (Aspergillus fumigatus, Aspergillus niger), Micofiti Vari 1 (Alternaria alternata, Chaetomium globosum, Cladosporium, Helminthosporium sativum).
MITES: Blomia Tropicalis, D. pteronysinnus, D. farina.
ANIMALS & VENOMS: Cat dander, Dog dander.