Skin prick testing (SPT) is one of the most commonly used allergy tests in children. As a Consultant Paediatrician with a special interest in allergy, I use skin prick testing as part of the allergy assessment for many of the children I see. This article explains how it works, what to expect, and how to interpret the results.
What Is Skin Prick Testing?
Skin prick testing is a quick, reliable and well-tolerated test for IgE-mediated allergy. It tests whether your child's immune system has produced IgE antibodies to specific allergens — foods (such as milk, egg, peanut, wheat) or environmental allergens (such as grass pollen, house dust mite, pet dander).
How Does Skin Prick Testing Work?
A small drop of allergen extract is placed on the forearm. A small lancet (a tiny plastic device with a fine tip) is used to introduce the allergen just below the surface of the skin. This feels like a light scratch — not a needle injection. Multiple allergens can be tested at the same time.
Two control solutions are also applied: a positive control (histamine, which should always produce a reaction) and a negative control (saline, which should not produce a reaction). These controls ensure the test is working correctly.
After 15–20 minutes, I will measure any skin reactions (wheals) that have developed. A positive result produces a small raised bump, similar to a mosquito bite. The size of the wheal is measured and compared to the controls.
Is Skin Prick Testing Painful?
Most children tolerate skin prick testing very well. The lancet produces a very superficial scratch — most children describe it as feeling like a light touch rather than a needle. The main discomfort is the itching that occurs if a positive reaction develops, which resolves within 30–60 minutes.
For younger children, distraction with a favourite toy, book or snack can be very helpful. I am experienced in making allergy testing as comfortable as possible for children of all ages.
What Do the Results Mean?
A positive skin prick test result means that your child's immune system has produced IgE antibodies to that allergen — this is called sensitisation. However, sensitisation does not always mean your child will react to the food when they eat it. The results must always be interpreted in the context of your child's clinical history.
- Positive test + history of reaction to that food: Strongly suggests allergy. Management will be guided by the severity of previous reactions.
- Positive test + no history of reaction: May represent sensitisation without clinical allergy. Further assessment may be recommended to clarify.
- Negative test + history of reaction: Does not rule out allergy. Non-IgE-mediated allergy will not be detected by skin prick testing. Further assessment may be needed.
Preparing for Skin Prick Testing
- Stop antihistamines (cetirizine, loratadine, chlorphenamine) at least 3–5 days before the test
- Avoid applying topical steroids to the test site (forearm) for a few days before the test
- Your child can eat normally before the test
- Wear or bring clothing that allows easy access to the forearms
See also: What Happens During Allergy Testing? | Food Allergy Assessment
Dr Mugilan Anandarajan, Consultant Paediatrician (FRCPCH, MD). Also see: belfastallergyclinic.com | belfastchildrensclinic.com