Skin prick testing (SPT) information sheet

Contact the respiratory lab

The Children's Hospital at Westmead: 

Sydney Children's Hospital, Randwick:

Introduction

Skin prick testing is a safe and minimally invasive method of testing whether a patient has hyper-sensitivities to certain airborne allergens that may trigger respiratory symptoms. 

About the test

  • An allergy is an inappropriate immune response to a harmless substance (called an allergen), in which the immune system is prompted to release chemicals, such as histamine, that cause the symptoms of an allergic reaction.
  • SPT involves applying a drop of a saline solution containing the dissolved allergen onto the forearm. Allergens ranging from grasses, animal furs, moulds and dust mites, including two controls will be used during the test.
  • The scientist will then use a lancet to create a small ‘scratch’ on the skin at each site, allowing the allergen to enter the epidermal (outermost) layer of the skin where the reaction can occur.

Preparing for the test

In order to prevent the risk of false negative results, it is required for the patient to abstain from all oral antihistamines for 4 days prior to the test. 

On the day of the test

Step 1

The respiratory scientist will explain the test procedure to you and your child. Your child (depending on their age and level of comfort with the test) will either sit upright by themselves on a chair or on their parent/guardian’s lap.

Step 2

The scientist will then draw a picture on the patient to mark the placement of each allergen. A drop of each of the 20 allergen solutions will be applied onto the skin.

Step 3

The scientist will lightly scratch the skin at the site of the droplet. After a 10-15 min wait, the scientist will measure the reaction (if any) to each allergen.

Step 4

A positive (allergic) reaction will appear as a red and itchy raised bump known as a wheal. The size of the wheal does not indicate the severity of symptoms but shows the degree of sensitivity to the allergen.

Step 5

At the end of the test, calamine lotion can be applied to any wheals to reduce itchiness.

Things to consider

  • While SPT is minimally invasive, the process may be distressing for some patients, particularly those who are young and have a fear of hospital procedures.
  • If necessary, toys and videos may also be used as a distraction technique to help the patient to remain calm.
  • The test can be terminated at any time at the discretion of the child, parent/guardian or scientist.
  • If a patient is unable to remain calm, they may need to be held still in order to prevent injury to themselves or others during testing. 

Please note that this is only performed with consent from the parents/guardians and the test can be terminated at any time.