Antibodies are proteins created by the immune system (via the lymphocytes) which circulate in the blood and are designed to neutralise the antigen. It is the antibodies that trigger the release of the chemicals which produce the allergic reaction - swelling of the face, throat and respiratory channels, itching etc. Confusingly, these reactions can occur within seconds (as in the case of a Type 1 reaction) or not for up to 72 hours.
Antibodies fall into five main groups - IgA, IgD, IgE, IgG and IgM.
Although similar in structure a tiny section of some antibodies (IgE antibodies in particular) is ‘customised’ to the particular antigen it has been created to neutralise. The customised part is called the epitope and this ‘customisation’ allows the antibody to ‘bind’ or stick to that specific antigen and that antigen only.
The majority of allergy tests measure the number of antibodies (of various kinds) in the blood of the patient. If each antibody is (via its epitope) specific to the antigen it was created to neutralise, matching the antibody in the patient’s blood to an antigen should, in theory, lead the tester to the antigen (food, chemical, mould etc) causing the problem.
IgE antibodies - Type 1 Anaphylactic or Immediate Hypersensitivity
In the case of IgE antibodies this system does work fairly
When IgE antibodies bind to their antigen (or allergen) they trigger an immediate release of histamine which causes inflammation and tissue damage which, in turn, can cause dramatic respiratory, gastric or skin reactions including anaphylactic shock.
Identifying the substance to which the patient’s specific IgE antibodies binds de facto identifies the antigen.
The RAST or radioallergosorbent allergy test - uses IgE antibodies in the patient’s blood to identify Type 1 allergies.
RAST tests are available on the NHS and at some private allergy
clinics. They are reasonably accurate although they do throw up a significant number of both false positives and false negatives.
Skin prick tests
The alternative diagnostic test used by most mainstream allergists, skin prick testing uses a tiny drop of the suspect allergen (food, pollen, mould, dander, chemical etc) placed on the skin where a small scratch has been made to allow the allergen to penetrate.
The degree of allergenicity is assessed by measuring the size of the wheal which appears at the point of contact. When no
reaction is achieved with a skin prick, but an allergy is still suspected, the allergen can also be injected under the skin.
Skinprick testing is relatively simple to perform and, although most allergists will only use laboratory produced concentrates of allergens, it is possible to manufacture very specific solutions to test for uncommon allergens or allergic triggers.
(See Dr Harry Morrow-Brown’s website for more discussion of such tests.) Tests are available on the NHS and from private clinics.
These are used mainly to determine whether a skin condition such as dermatitis could have an allergic component. The allergen is placed on a pad which is taped on to the skin for 24-72 hours; the reaction is then assessed.
Patch tests are available on the NHS or from a dermatologist.
Sensitivity versus reactivity
The presence of antibodies, however, does not guarantee an allergic reaction. There are occasions when a patient carries a very high number of antibodies to a specific substance (eg - is sensitised to it) yet does not react to it.
For example, someone who works with cats might have a high number of antibodies to cat dander because they are in constant contact with them, yet not react to them. Dr Hugh Sampson investigated this subject in some detail in Foods Matter in June 06 - click here to read the article.
This means that in cases where avoidance of the suspected allergen may cause serious lifestyle disruption, the test finding needs to be validated by a controlled food or substance trial.
Elimination and challenge
Any of the tests mentioned so far will, effectively, need to be validated by elimination and challenge - avoiding the suspect food or substance for a period (usually three to six weeks) and monitoring whether the symptoms improve, and then ‘challenging’ the patient by having them eat the food or come into contact with the substance once again and seeing whether the symptoms reappear.
Obviously, when dealing with Type 1 reactions, the ‘challenge’ needs to be carried out under controlled medical conditions so if the patient suffers a serious reaction professional help is at hand.
Some allergists would regard elimination and challenge as the only really reliable allergy test and, having taken a detailed patient history, would go straight for it. There is certainly no doubt that it is the most reliable and can be tailored most precisely to the individual’s needs.
However problems arise when more than one allergen is involved (so eliminating only one may not achieve any significant improvement in symptoms) and where the reaction is delayed, so that it is difficult to attribute a specific reaction to a specific allergen.
It is particularly difficult when dealing with environmental allergens where it may be almost impossible even to identify substances that should be avoided.
If there are multiple symptoms and a number of foods appear to be involved some practitioners will advise a few-foods diet. This reduces food intake to the most basic and simplest foods (lamb, pear and rice are normally thought to be the least allergenic foods). If symptoms improve, then ‘new’ foods are added one by one, and symptoms monitored carefully thus, over the course of time, identifying the culprit foods.
However, this is a really hard regime to follow and requires great discipline and patience on the part of the patient and the doctor. There is also the risk of nutritional deprivation if the diet remains too limited for too long.
For a short article by Dr Morrow Brown click here; for a comprehensive clinical protocol see Dietary Management of Foods Allergies and Intolerances by Dr Janice Joneja published by JA Hall Publications.
Nonetheless, if you can stick with it, an elimination and challenge diet will identify problems caused not only by foods which trigger a Type 1 response but foods which trigger a whole range of other reactions which may be set off by other anti-bodies or in which antibodies may not be involved at all.
Compliance - or lack of it...
It is when faced with the prospect of a lengthy and restrictive elimination diet or avoidance regime that the average sufferer looks for a test which will identify the problem food (or mould, or pollen, or chemical) without them having to spend months struggling with a severely restricted diet or lifestyle.
Although there are a number of tests which claim to do this on the market, many of which have proved hugely helpful to a large number of grateful patients, none of them have, as yet, been validated to the satisfaction of most conventional allergy specialists. These range from antibody (IgG) and leukocyte blood tests, through energy based assessments to practitioner mediated tests such as kinesiology.
IgG antibody testing
The most widely used - and argued over - of these are IgG blood tests, which use an enzyme-linked immunosorbent assay or ELISA system.
The question at issue is whether the immune system creates, or ‘customises’, specific IgG antibodies to substances that it finds problematic in the same way that it creates IgE ones - or whether IgG antibodies have no specific relationship to any one food or substance and therefore their presence is no indication of a problem with that food or substance.
However, recent research carried out by Dr Anton Emmanuel and his colleagues suggests that there may indeed be a specific link between the presence of IgG antibodies and bowel conditions such as Crohn’s disease and irritable bowel syndrome and that these antibodies may be linked to specific foods.
Based on the assumption that this relationship does exist, IgG testing is on offer via a home skin prick test kit - you can order it on line, on the phone or buy it from a chemist. The two companies below are the leading UK suppliers.
Both of these companies offer a relatively cheap test which will indicate whether or not you are likely to be sensitive as well as more comprehensive and wide ranging tests. Test results suggest foods (or substances) that should be completely avoided, those that should be treated with care and those that are problem free. The test results usually come with comprehensive nutritional advice.
Cambridge Nutritional Sciences
CNS offer a range of ELISA based IgG food intolerance tests ranging from a £20 Food Detective kit which you can use at home (like a pregnancy test) and which will tell you whether or not you are food intolerant, through a 40 foods (£99), 60 foods (£149), 120 foods (£199) to a 200 foods test (£275).
They also offer a vegetarian food test (£149) and a herbs and spices test (£99).Apart from food intolerance CNS also offers tests for anaemia, candida, coeliac disease, helicobacter, intestinal parasites, osteoporosis, rheumatoid arthritis and thyroid.
Yorktest offers an ELISA based Intolerance Indicator for £17.50 which will tell you whether or not you are intolerant and then a 113 foods test for £242.50 (to on-line buyers).
They also offer a homocysteine test (possible indicator of heart disease or stroke), a house dust mite detection kit and an IgE testing kit, although this requires blood sample drawn by a health professional.
0800 074 6185
First Published in July 2002
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