If it is suspected that you have an allergic condition then you may be referred for testing.
These tests can be undertaken in a variety of ways. Your doctor or allergy specialist will select the test most suitable for you.
Depending on the outcome of these you may be given advice on how to avoid your triggers.
Skin prick test
This type of test can be used to confirm the presence of a variety of different allergies including those caused by food and those that are inhaled.
The test can be carried out in both children and adults and is usually administered to the forearm, although the upper back and thigh may be used in some circumstances.
Small, painless punctures are made to the area through which a tiny amount of each allergen is introduced to the skin. Each puncture is marked with a code in order to keep track of which allergy causes what reaction.
If an allergic reaction takes place the skin may become red, raised and itchy. A trained specialist will then interpret the results at around 15 minutes to let you know whether or not you have an allergy. The overall process takes around 40 minutes.
A sample of blood can be taken to check for the amount of Immunoglobulin E (IgE) antibodies produced in response to a suspected allergic reaction.
The blood is sent to a laboratory and the results are reviewed by a specialist. The outcome usually takes between 7-14 days to return.
This test cannot determine how severe an allergy may be and so cannot be used to diagnose potential anaphylaxis.
Patch tests are carried out by dermatologists in order to establish which allergen is triggering a skin reaction such as eczema or dermatitis.
The test involves small aluminium discs that are each coated with a concentrated patch of the various potential trigger substances. They are then placed in direct contact with your skin, usually on your back.
The area used for the test should ideally be free from eczema and you may also be advised to stop the use of medications such as steroid creams and tablets as they could conceal a reaction.
The test usually comprises of the most common allergens alongside some that you bring from your own home or office. They might include cosmetics, toiletries or materials.
The patches are kept in place for around 48 hours at which point they will be removed and assessed by a specialist. Reactions usually present themselves through irritated skin which is quite often itchy.
Oral food challenge (OFC)
This type of test is usually chosen when blood or skin prick tests have been inconclusive.
There is a chance that this test might cause a more serious reaction which requires medical attention. For this reason the test is usually carried out in surgery or at a hospital, where the appropriate support and equipment is available should they be required.
During this test measured doses of the potential food allergen are fed to the patient. The test initially starts with a very small dose which should not provoke a reaction. The patient will be observed for an amount of time following each dose of food and if no response is noted the next dose will be given.
If at any point a reaction does take place, the test will be stopped.
The test can be administered following a number of methods:
- Open food challenge. In this test, both the patient and the doctor are aware of what allergen is being tested. This version of the test is chosen when the patient’s nerves are unlikely to alter the outcome.
- Single-blind food challenge. Only the doctor is aware of what allergen is being tested.
- Double-blind, placebo-controlled food challenge. The allergen food is used alongside a placebo and neither the doctor nor the patient are aware of which is which. This is in order to achieve objective results that have not been influenced by the doctor’s unintentional indications or the patient’s anxiety.
Symptom / food diary
Another method which can help you to identify your food allergens is keeping a food or symptom diary. This consists of keeping a record of the following:
- Every item of food or drink that you consume
- At what time you consumed them
- Any activities that you were taking part in at the time
- The nature of any symptoms that have occurred and how long they lasted for
- Treatment sought
- Treatment efficacy
The information you gather should highlight any links between certain types of food and an allergic response. Your doctor will use this information to come up with the best possible treatment plan for you and also provide you with dietary advice. This way you can adapt your diet and hopefully avoid any unpleasant allergic reactions in the future.