What is Skin prick testing?
Skin prick testing is an allergy test used to identify allergens responsible for triggering symptoms in allergic diseases. Whilst patch testing is a useful diagnostic test for patients with allergic contact dermatitis, skin prick testing is useful in the diagnosis of other allergies such as hay fever allergy, food allergy, latex allergy, drug allergy and bee and wasp venom allergy.
Skin prick testing with a battery of routine allergens is an important basic procedure in diagnosing allergic diseases. It is simple, carries low risk and is inexpensive to perform.
Indications for doing skin prick testing
Skin prick testing is most often used to demonstrate atopy. Atopy is characterised by an overactive immune response to environmental factors and has a strong genetic component. It usually manifests clinically as one or more of the characteristic disorders of asthma, eczema, or hay fever (rhinitis). The results from skin prick tests can be used to guide the management of patients with asthma and hay fever, eg, desensitisation to a certain allergen, removal of a family pet, removal of carpets, avoidance of certain foods. It is also useful in patients with bee and wasp stings, and acute urticaria, especially if immunotherapy is being considered.
Skin prick testing is generally unhelpful in the investigation of atopic dermatitis, chronic urticaria and angioedema, food intolerances, dermatitis herpetiformis, and nonspecific rashes.
Overall, skin prick tests can provide confirmatory evidence for a diagnosis made on the patient's history and clinical condition.
Skin prick testing results
Reactions are assessed by the degree of redness and swelling and the size of the wheal produced. The wheal has a white, raised edge that surrounds the swollen red central area of any skin reaction. It usually takes about 15-20 minutes to reach a maximum size, and thereafter fades over a few hours.