We use a number of different techniques and clinics to test for allergies which are listed below.
Skin prick test
A small needle is used to gently prick the skin through a droplet of fluid containing a known allergen. If the skin around the needle prick becomes itchy, red and swollen, in combination with a suggestive history, we are likely to be able to confirm your allergy. You will need to stop taking antihistamines for at least 48 hours before the test.
Specific IgE blood test
This is another way to test for allergies by taking a sample of blood and measuring the allergic antibodies (chemicals) in the bloodstream. It is suitable for patients unable to have skin prick tests, for example, those who cannot stop taking antihistamines or who have severe skin conditions, or where further information is needed after skin prick testing.
You will need to bring in foods that you suspect you are allergic to which we will use for testing. A lancet is used to prick the food and then, the same lancet is used to prick your skin. After 15 minutes, the site is inspected to check for any reaction such as swelling.
The challenge test is only used in very limited circumstances and involves introducing a suspected allergen, such as a particular food or drug, to see if a reaction occurs. The patient is given increasing amounts of the allergen – usually by mouth. If a reaction occurs, at any stage, the test is stopped.
This test is performed by a specialist nurse and consultant, when other tests have not been able to confirm a diagnosis and when the outcome is clinically important. Challenge testing can only be performed at special units where we have full medical observation facilities including resuscitation equipment and medical and nursing cover.
Patch testing identifies allergens causing contact dermatitis (a delayed allergic reaction on the skin). Strips already prepared with the allergens are placed on the patient’s skin, normally on their back. The strips remain on the skin for 48 hours and are assessed after 72 hours. The area is examined for evidence of hypersensitive reactions.
Patients will need to ask your GP or hospital doctor to refer you to this service via dermatology at St Bartholomew's.
Adrenaline auto-injector pen training
Anaphylaxis is a severe allergic reaction with airway obstruction (difficulty in swallowing or breathing) or a drop in blood pressure (feeling faint or collapsing). The immediate treatment for this is adrenaline. If you are at risk of anaphylaxis, you will be prescribed an adrenaline auto-injector pen. Our nurse specialist will give you advice on using one, using a ‘dummy’ pen for demonstrations.
There are three widely-used types of auto-injector pen - the Epipen, Anapen and the Jext. They contain a single dose of adrenaline that can be injected into the body. The adrenaline helps open to the airways so that you can breathe and reverse any fall in blood pressure.
After an extreme allergic reaction, you should always be seen in an emergency department and referred on to an allergy clinic.
One-stop clinic for allergies
Patients are assessed by a consultant, receive allergy testing, and are given a self-management plan with input from our specialist dietitian and nurse specialist. This can include an exclusion diet or advice on avoiding allergens such as dust mites in the home. Our aim is to see and diagnose most patients in just one visit, with further follow-up sessions readily available if necessary.
This clinic is based at St Bartholomew's. Contact us on 020 3765 8096.
Desensitisation (allergen immunotherapy)
This treatment may be helpful for patients with severe allergic rhinitis or venom allergy. A consultant will assess your suitability, and then if appropriate, you will have a course of treatments, using the allergen that you’re sensitive to, over a three year period.
We provide both subcutaneous injections (under the skin) and sublingual tablets (under the tongue). For the first three months, you will need to visit every week (for an hour), then after that, you will need to come in every month. Patients are closely monitored after each injection, in case there are any side effects.
The aim is to help the body tolerate the allergen so that in the long-term any reaction is not so severe and medication can be reduced. Desensitisation may be used to help patients who have failed to respond to conventional treatment.
The clinic is run by specially trained nurses from the adult allergy clinic at St Bartholomew's. Contact us on 020 3765 8096.