Skin Prick Allergy Testing

An allergy is an abnormal immune response to commonly occurring substances (that are not harmful in themselves). These include foods, inhalants (pollen, dusts, and animal dander), insect bites and drugs. Skin prick testing is a simple test used to diagnose allergic responses. Skin allergy tests also have the advantage of providing results almost immediately.

Test Duration

Approximately 15 minutes

Test Preparation

You may generally continue with your normal routine. However, there are some points to note to improve comfort and ensure accurate results:

Antihistamines should be withheld for a minimum 72 hours prior to testing.

Antidepressants such as doxepin, other tricyclics, and tetracyclics have antihistamine activity and may need to be withheld for 1-2 weeks or more.

Topical moisturisers do not reduce prick test reactions but may cause extracts to run or disperse which creates a practical difficulty.

Test Procedure

The test is performed on the inner section of the forearm. First a permanent marking pen is used to write numbers on the skin. Next a drop of a specific allergen corresponding to each number is placed adjacent to each number.

A small superficial break is then made in the skin within each drop to allow the reaction to occur. During the insertion of the lancet blood should not be drawn, but can occur when the patient is on blood thinners, the skin is fragile due to some drugs or age, or the lancet is applied too hard.

Once the skin is broken, a timer is turned on and the patient is observed for 15 minutes. During this time period one or more of the areas may become itchy but it is important not to scratch the area.

If the result is positive, meaning you react to that allergen, the area becomes raised, red and itchy. This reaction will nearly always occur in one area known as the positive control, which checks if your body has the ability to react to the test.

After 15 minutes, the size of the reaction is measured with a ruler. If the diameter is greater than 3 mm then the test is positive. After this time if the reaction continues to irritate you, a steroid cream can be applied. After the test you can participate in any form of activity.

Risks involved

Skin prick testing is a low risk procedure. The risk of an adverse reaction is accepted to be less than 1% and can include: nausea, fainting, near fainting and malaise. This risk is increased if you have asthma, and particularly if it is currently active.