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How are allergies diagnosed or tested?

Thursday 3rd April

In today’s highly connected society, many of us use the internet or social media to research symptoms and ‘conclude’ that we might have a particular allergy.

Of course, the safest way to clear up, once and for all, if you have an allergy, is to consult your GP – who will then recommend the best course of action to take. Your GP will talk through your symptoms with you – find out about what questions you could ask your GP

Your GP may refer you for allergy testing – which should only be carried out following full consultation and by a healthcare professional qualified in allergy.

Skin testing

‘Skin prick testing’ or SPT is a fast and safe way of testing if you are allergic to any specific allergens, allowing results to be seen within 15 to 20 minutes.

The SPT introduces a tiny amount of allergens into the skin, usually on the inner forearm although sometimes the back or thigh may be used, in order to elicit an allergic response – such as a bump or redness. This is done in a controlled environment with professional clinicians who will discuss your medical history with you to identify the most appropriate allergens to test.

The SPT can be carried out on any age group.

Blood tests

If skin prick testing is impractical, for example when a patient has eczema, then blood testing may be used.

A small sample of blood will be taken - usually from a vein in the arm - and sent for testing in a laboratory, with results often available within 7 to 14 days.

The laboratory will test for the amount of something call ‘IgE antibody’ in the blood, the results of which helps clinicians calculate the form of allergy.

Patch testing

A patch test can be effective in identifying skin-related allergies, such as allergic causes of eczema/dermatitis or skin reactions to drugs. Relevant patches containing allergens - following consultation with clinicians - will be applied on patches of normal skin and left in place for 48 hours. Following removal, the skin will be examined and, if needed, further patch testing takes place.

This can be an effective way to help patients know what chemicals to avoid, such as specific types of hair dye.

Allergy Challenge

The above tests can have their drawbacks or have inconclusive results, particularly in food allergy, so healthcare professionals can also try ‘Allergy Challenge'. The Allergy UK website states: “Challenge tests are always undertaken in hospital under close medical supervision where resuscitation equipment and emergency medication are available in case a severe reaction occurs. This is a precaution, but one that is taken very seriously by staff involved.” The Allergy Challenge looks to introduce allergens via oral methods and is carefully controlled and monitored – only being performed in a hospital environment.

Useful Links

NHS Choices talks about allergy testing via the NHS.
Boots WebMD is also a useful resource.