Information on testing for allergies
Allergies and intolerances can cause serious problems and currently it is thought 1 in 4 people suffer with some sort of allergy. There are many substances we come into contact with that can trigger and cause allergies. Examples of these include, but are not exclusively confined to; food, house dust mites, pollen, animals, moulds, drugs (e.g. antibiotics), lanolin, metals, solvents, household chemicals.
If an allergic reaction is suspected, you will need to identify the exact allergen causing it. To do so you should make an appointment to see your doctor, nurse or health visitor who will be able to advise you about being tested.
Allergy testing can be done both privately and through the NHS and the type of test that is carried out will depend upon your symptoms or the condition of your skin. The main tests that are available are:
- Skin prick test
- Blood test
- Patch test
Skin Prick Test
A skin prick test is usually the first test to be done when looking for a potential allergen. It is a quick, painless and safe test and you get the results within about 20 minutes. When performed correctly it has a high degree of accuracy and can be carried out safely on anyone from 4 months old.
Your skin is pricked with a tiny amount of the suspected allergen to see if there is a reaction. Up to 24 allergens can be tested at any one time. If there is a positive reaction to an allergen the skin around the needle prick will very quickly become itchy and a red wheal (swollen mark) will appear. A negative skin test will generally mean that you are not sensitive to that allergen.
A blood test will be performed which will measure the amount of Specific IgE circulating in the blood. IgE are antibodies which travel to your cells and release chemicals which produce an allergic reaction. The level of IgE antibodies in your blood is important as it gives an indication of your body’s response to a suspected allergen. However the blood test cannot give a clear indication of the severity of an allergy, simply whether a person is likely to be allergic or not.
Blood tests are generally used if:
- There is a risk of an anaphylactic reaction; this is a potentially life threatening medical emergency. Symptoms of anaphylaxis include itchy skin or a raised red skin rash, swollen eyes, lips, hands and feet, feeling lightheaded or faint, swelling of the mouth, throat or tongue, wheezing, abdominal pain, nausea and vomiting, collapse and unconsciousness. If a person experiences any of these symptoms, help should be sought immediately from a qualified medical professional.
- If there is extensive eczema which will make skin prick testing hard to carry out.
- Antihistamine medication cannot be stopped due to the severity of the symptoms. (Histamine is produced by your body in response to a potential threat such as an allergic reaction. Antihistamines work by altering the way your body’s cells respond to histamine)
- Unusual and rare allergens are suspected.
The results generally take 7-14 days to come back from the laboratory and will be interpreted by a qualified medical professional who will look at the results alongside your medical history. Over 400 specific allergens can be tested for in blood tests.
This test is used in cases of contact dermatitis (eczema) where allergies are suspected. It can test for contact allergies to rubber, nickel, lanolin, hair dyes, cosmetics, perfume, preservatives and skin medications. 2-3 weeks before having a patch test you will need to stop using steroid creams (as these may slow down any potential reaction you may have to an allergen) and any eczema will need to be under control.
The allergens are spread onto special discs which are placed onto the skin (usually the back) and held in place by hypoallergenic tape. The patches will be given a number; will remain on the skin for 48 hours and need to be kept dry. The patches will then be removed and the skin is examined with any redness or swellings noted. The skin is then re-examined after a further 48 hours for any remaining local redness or swelling.
The interpretation of the results will be carried out by the hospital dermatology department.
When choosing how and where to be tested for allergies it is important to see a reputable and trained specialist. An internet search for allergy testing will bring up many non-conventional commercial allergy testing kits. These kits include hair analysis tests, applied kinesiology (a test which measures changes in muscle strength before and after exposure to a potential allergen) and VEGA tests (test measures the electromagnetic fields produced by the patient when a suspected allergen is brought near to the patient). Many are not recommended by doctors since there is little scientific evidence to support them.
Sources used in writing this article are available on request.
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Information written by the talkhealth team
Next review: 30 July 2022