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Allergy

Tests used in allergy diagnosis

Skin prick allergy test

Skin prick testing 


This is a universal allergy test and often used to find out what is causing an allergy. It gives results on the same day of your visit and is a very helpful first step. However, we can only do skin prick testing if you have not taken any antihistamine tablets or liquid for at least three days. 

Skin prick testing involves placing a drop of liquid onto the skin of the forearm and pricking through it with a sharp type of pin called a lancet. Most people coming to the allergy clinic will be tested to find out whether they are sensitive to common airborne allergens, such as: 
  • grass
  • tree and weed pollen
  • cat and dog hair
  • moulds
  • house dust mites
  • certain foods, such as nuts and apples. 


Specific immunoglobulin E (IgE) blood test


We can test for many different foods by taking a blood sample. This is helpful when people have taken antihistamines or for confirmation of skin prick testing results. We can also test for individual proteins in some foods, such as peanuts and hazelnuts. This is often called component testing and helps us find out whether someone has a food allergy or a pollen allergy which is causing cross-reactions to certain foods.


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Dr Isabel Skypala

Oral food challenge 

Oral food challenges are tests that use suspected food allergens. 

  • Traces of the food are initially rubbed onto your lower lip;
  • Then traces are placed inside the lip;
  • Then increasing doses of the food are given to you every 1015 minutes until, finally, you are able to consume a substantial amount of the food without allergic reaction. 

The foods that we most commonly test are peanuts, tree nuts and shellfish. The main symptom that you will experience, if you are sensitive to the allergen during the food challenge, is itching in the mouth and throat. You may also experience wheezing and respiratory difficulties, and sometimes patients can experience more severe symptoms, such as swelling and hives. 

It is essential that the tests take place under close medical supervision because sometimes patients with negative skin prick and blood tests to a food can have an unexpected positive reaction during the challenge.


Drug challenge testing


Before you have a drug challenge, certain tests will be carried out. These are usually skin prick tests, using a diluted liquid preparation of the drug, a drop of which is placed on your forearm and pricked through. If this test is negative then slightly deeper skin tests called intradermal tests might be carried out. If this is also negative then a drug challenge is undertaken. All drug challenges are carried out under medical supervision by a highly experienced clinical team trained in the early recognition and treatment of allergic reactions. They involve giving you increasing doses of the drug over the period of a couple of hours and monitoring closely for symptoms. 


Royal Brompton

Sydney Street,
London SW3 6NP
Tel: +44 (0)20 7352 8121

Harefield

Read about the allergy clinics held by the Trust