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Diagnosis and Testing

What is Allergy?

The term allergy is used to describe a particular response by the bodys immune system to a substance

in the environment, such as pollen or foods. In most people, the body recognises these substances as

harmless. However, some people have a tendency to develop allergy (this is called atopy). In these

people, exposure to these substances (called allergens) results in the production of IgE antibodies

against the allergens. This process is called sensitization. However, at this stage, no symptoms are

noted.

The next time the person meets this substance the antibody reaction will cause the release of certain

chemicals into the body. These chemicals cause the symptoms of allergy.

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 be used to describe a reaction produced

by the immune system to a normally harmless substance.

Sensitivity is an exaggeration of a normal side effect produced by contact with a substance. For

example, the amount of caffeine in a single cup of coffee may cause palpitations and trembling in a

sensitive person, where this would normally only occur after far higher doses of caffeine.

Intolerance happens for a variety of reasons, for example, because your body does not produce

sufficient quantities of a particular enzyme/chemical, which is needed to break down a food and aid

digestion. However, intolerances do not involve the bodys immune system and cannot, therefore, result

in life-threatening allergic reactions.

How Do You Know If You Have an Allergy?

The most useful tool in deciding whether someone is allergic is to take an allergy history. A good allergy

clinician can usually identify the likely allergens from the history alone, and allergy tests may not be

needed. However, there are occasions when tests can be useful to confirm the diagnosis. 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 or whether some other process is involved.

What Allergy Tests are Available?

The type of test to be carried out will depend upon your symptoms, the condition of your skin, and any

medication you are taking.

The best allergy test (known as a gold standard test) i s to expose a person to the allergen concerned,

such as a food. This is known as anAllergy Challengetest. Since this may cause an allergic reaction, such

a test should generally only take place in a specialist clinic where appropriate medical facilities are

available to manage any reaction.

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Unfortunately, the allergy challenge test can be complicated to organise and may not be safe for you.

Therefore, other tests which look for the presence of IgE antibodies are often used. These tests look for

sensitisation rather than true allergy, as some people will be sensitised to the allergen but not have

developed the allergy (see above). This is because in these people, the degree of sensitisation which has

occurred is not sufficient to trigger an allergic reaction. Indeed, in some cases, such a person may

become allergic if they stop eating a food to which they are sensitised.

It is for this reason that allergy tests need to be interpreted by a healthcare professional qualified in

allergy, who will interpret the results in light of the patients history in order to determine whether

someone is allergic. This also explains why it is important not to test everybody for every known

allergen, as it can be difficult to interpret the results.

Tests which look for IgE antibodies includeSkin Prick Testingandblood testsfor specific IgE antibodies.

Patch Testingcan be useful in cases of contact dermatitis (eczema) where delayedtype allergy is

suspected to be a trigger. They are not helpful in the diagnosis of immediate-type allergies, including

most food allergies.

Other (non-conventional) allergy testsare not considered to be relevant, standardised or repeatable

and are considered to have no place in the diagnosis of allergy. These include Applied Kinesiology

(measures muscle strength), Auricular Cardiac Reflex Method (measures strongest pulse at wrist), Hair

Analysis, Leukocytotoxic Tests and Vega Testing (measures the electromagnetic fields produced by the

sufferer).

IgG blood tests are one type of non-conventional test. These are different from blood tests for specific

IgE, and are of no use in the diagnosis of true allergy.

Can We Test For Food Intolerance?

Some practitioners use IgG blood tests in helping to diagnose food intolerances, such as those which

may cause symptoms in some cases of migraine, arthritis and irritable bowel syndrome. However, the

data is not scientifically robust and most allergy specialists consider IgG blood tests to be unhelpful in

these circumstances. The gold standard test for food intolerance remains the elimination and challenge

diet (see Food Intolerance section).

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