Allergy Clinic

Allergy testing

Before appreciating what allergy testing is and what it means, we must first consider the questions which are asked by many sufferers, their families and carers.

What is Allergy?

The term allergy is used to describe a response, within the body, to a substance, which is not necessarily harmful in itself, but results in an immune response and a reaction that causes symptoms and disease in a predisposed person, which in turn can cause inconvenience, or a great deal of misery.

Allergy is extremely widespread and affects approximately one in four of the population in the UK at some time in their life.

Each year the numbers are increasing by 5% with as many as half of all sufferers being children.

What is the difference between Allergy, Intolerance, and Sensitivity?

Although the word “Allergy” is commonly used to describe any unpleasant reaction to a drug, food, insect sting, or chemical, this can be misleading. The word should only really be used to describe a reaction produced when the body meets a normally harmless substance, which has been “remembered” from a previous exposure and subsequently produces the “IgE” antibody.“Sensitivity” is a reaction to a substance, which is an exaggeration of a normal side effect produced by that substance.

For example, reliever inhalers used in asthma, if given at too high a dose in a particular individual may cause them to “shake”.“Intolerance” happens when unpleasant symptoms occur after eating a substance, which your body cannot handle because the digestive system does not produce sufficient quantities of a particular enzyme/chemical, which is needed to break down the food and aid digestion, eg wheat intolerance.

The causes of symptoms need to be correctly diagnosed so that the management and treatment for either allergy, sensitivity or intolerance can be appropriately taken.

How do you know you have an allergy?

Often the history can help towards identifying allergens. Even if you know what is causing your allergic reaction, you may still need to have confirmation of the offending allergen. This is especially important if you have had a severe reaction and if there is any confusion as to whether your symptoms are caused by a true allergy (involving the production of IgE) or whether some other process is involved.

Allergy testing can help clear any doubts.

As stated at the beginning (1 in 4) 25% of the population will at some time in their life see a doctor because of an allergy, as a consequence and frequency of these problems allergy testing is becoming increasingly sophisticated.

What allergy tests are available?

The type of test to be carried out will depend upon your symptoms or condition of your skin and are described as follows:

BLOOD TEST

Blood tests measure the amount of IgE circulating in the blood, that the immune system has produced against a suspected allergen.The test is carried out on a small sample of blood, which is usually taken from a vein in the arm, using a fine needle and a small syringe, causing minimal discomfort. The sample is then sent to a hospital laboratory and the results are available in 7 to 14 days.

PATCH TESTING

This test is performed in cases of contact dermatitis (Eczema) where allergy is suspected.The allergens are prepared in appropriate concentrations in white soft paraffin (e.g. Vaseline) and are then spread on to discs, 1 cm in diameter.

The discs (which are usually made of a special metal, cannot themselves provoke a reaction) are placed on the skin, usually on the back, and are kept in place by hypoallergenic tape.

The skin is coded appropriately and the patient is asked to keep the skin dry. The patches are left in place for 48 hours.

After which time the discs are removed, the skin is examined and any redness or swellings are noted. The skin is re-examined after a further 48 hours for any remaining local redness or swelling.

The interpretation of this form of testing is not as simple as it sounds and tends to be carried out by dermatology department in hospitals. The symptoms of contact dermatitis need to be brought under control before patch testing can be carried out, otherwise the results will be unreliable.

Steroid creams need to be stopped for 3-4 weeks before testing as they may suppress the test response.Any professional interpreting skin, blood or patch tests must first interpret the results in the light of the patient’s history. No test should be read in isolation.The Canterbury Skin and Laser Clinic offers both blood tests and patch tests if indicated.

OTHER (NON-CONVENTIONAL) ALLERGY TESTS

The following tests are not regarded by conventional medical practitioners to be relevant, standardised or repeatable and are considered to have no place in the diagnosis of true allergy.

Applied Kinesiology – measures muscle strength.

Auricular Cardiac Reflex Method – measures strongest pulse at wrist.

Hair Analysis – hair tested for medical problems.

Leukocytotoxic Tests – white blood cells mixed with suspected allergen and observed under a microscope.

Neutralisation-Provocation Testing – a specific dose of neutralised allergen drops are placed under the tongue.

Vega Testing – measures the electromagnetic fields produced by the sufferer. If in doubt, always request evidence of the results of approved clinical trials..