Skin Prick Test (SPT)
Skin Prick Test (SPT) for Allergies:
A Skin Prick Test (SPT) may be recommended to assess your child’s allergies. This guide explains what SPT involves and how it is performed.
Why is SPT Needed?
The Skin Prick Test is a precise method to identify specific substances, known as allergens, that might trigger an allergic reaction in your child. This test is beneficial for detecting both food and environmental (aeroallergen) allergies and can help monitor the progression of allergies, especially food allergies.
What Allergens are Tested?
The most common allergens tested are aeroallergens, which are present in environments like home, school, or outdoors. Indoor allergens often include dust mites, molds, cockroaches, and pet dander (such as cat or dog). Outdoor allergens include pollen from trees, weeds, and grasses.
For food allergies, a variety of foods can be tested, including milk, egg, soy, nuts (like peanuts, cashews, walnuts, almonds, and pistachios), fish, and seafood. If you suspect an allergy to a specific food, you can bring a small piece of it to the clinic. We can test it using a “prick-prick” method by pricking the food and then lightly scratching your child’s skin with it. Please pack the food separately, without mixing it with any other substances.
How is the Test Done?
SPT is typically performed on the forearm or sometimes on the upper back. A small drop of each allergen is applied to the child’s skin, and the skin is lightly scratched with a lancet to introduce the allergen beneath the surface. Many allergens can be tested simultaneously by repeating this process. If you’ve brought food to test, we’ll prick it with a lancet and then apply it to your child’s skin.
After 15 minutes, we check for the reaction, which can be either:
- Positive Reaction: An itchy, raised bump (or “wheal”) forms where the allergen was applied, surrounded by a red area called a “flare.” This “wheal and flare” reaction typically peaks within 15-20 minutes before fading. A positive reaction suggests your child may be allergic to that allergen.
- Negative Reaction: No significant “wheal and flare” reaction appears, suggesting your child is not likely allergic to that allergen.
Does the SPT Hurt?
Skin prick tests generally do not cause pain, as they only involve the outer skin layer (epidermis), which lacks pain fibers and blood vessels. Children may feel a slight pin-prick sensation. If positive, the reaction may feel itchy, but this typically subsides shortly.
When are Results Available?
SPT results are available within 15 minutes.
Are There Any Risks?
Apart from minor, localized itching where the test was performed, there are typically no issues. If needed, a cold compress or a single dose of antihistamine can relieve itching, although it usually subsides on its own. Severe allergic reactions to skin prick tests are extremely rare.
