What is the Significance of IgG Antibodies and Testing?

I recently highlighted my misgivings about the claims of sound science or clinical validation for IgG testing for food intolerance. Dr. de Asis gives a very helpful and clear overview of food allergy, intolerance and testing. Similarly, Dr. Minocha offers an fine overview of food allergy and tolerance.

I thought that it might be helpful to quote the position of some professional organisations on the topic of IgG significance and testing.

The American Academy of Allergy, Asthma and Immunology commented on the significance of IgG anti-allergen antibodies in September 2006. They observed that a number of commercial labs claim to be able to measure IgG antibodies against common substances: they questioned the clinical significance of the findings. Although this piece probably refers to labs in the US, experts question whether

commercial assays actually measure the IgG antibodies that they report. Also, even if the assays are measuring IgG anti-allergen antibodies, the clinical significance of such antibodies is certainly not clear.

Further comments highlight the controversies surrounding the significance of IgG antibodies. Some researchers argue that the current state of knowledge indicates that IgG antibodies may have a protective role rather than be evidence of harm.

There has been a long-standing debate about the significance of "atypical" (IgG4) anti-allergen antibodies with more observers stressing a possible down-modulating rather than a pathogenic role in allergic disorders. The significance of IgG anti-food antibodies is particularly uncertain since the sera of many children with such antibodies in their serum tolerate the foods in question perfectly well. [Emphasis added.]

The Australasian Society of Clinical Immunology and Allergy (ASCIA) has made a statement on the topic of IgG testing for the diagnosis of food intolerance:

IgG antibodies to food are commonly detectable in healthy adult patients and children, independent of the presence of absence of food-related symptoms. There is no credible evidence that measuring IgG antibodies is useful for diagnosing food allergy or intolerance, nor that IgG antibodies cause symptoms. The exception is that gliadin IgG antibodies are sometimes useful in monitoring adherence to a gluten-free diet patients with histologically confirmed coeliac disease. Otherwise, inappropriate use of food allergy testing (or misinterpretation of results) in patients with inhalant allergy, for example, may lead to inappropriate and unnecessary dietary restrictions, with particular nutritional implications in children. [Emphasis added.]

ASCIA investigate several unorthodox techniques for the diagnosis and treatment of allergy, asthma and immune disorders. They conclude:

Treatment based on inaccurate, false positive or clinically irrelevant results is not only misleading, but can lead to ineffective and at times expensive treatments, and delay more effective therapy. Sometimes harmful therapy may result, such as unnecessary dietary avoidance and risk of malnutrition, particularly in children. For example, Rona and Chinn found that around one half of parents who thought that their child was food allergic or intolerant altered their child's diet, but only one third sought medical advice, and that some children were 4cm shorter than controls. Unnecessary environmental and chemical avoidance, creating a perception of organic illness where none exists, or advising physical interventions when psychosocial factors are the source of symptoms, can impact on employment and social functioning. [Emphasis and link added.]

Although the British Society of Allergy and Clinical Immunology (BSACI) does not have a formal position statement, a former president, Prof. Kay, wrote the following in his written evidence to a parliamentary Select Committee on Health:

good allergy practice is evidence-based and that, as in other branches of medicine, allergy tests and treatment require rigorous scientific validation. At the time it was pointed out that there was a very wide sale and use of highly dubious allergy tests which could lead to wrong diagnosis, inappropriate treatment and the institution of nutritionally inadequate diets which can be harmful, especially to children...

...a number of other unsubstantiated tests which are widely available but have never stood up to any real scientific scrutiny. These include serum IgG antibodies for food allergy ("Yorktest"), iridology, applied kinesiology (muscle testing), cytotoxic food testing—ALCAT, electrodermal skin tests—VEGA testing, ELISA/ACT and hair analysis.

Thus I fully support the Evidence to Select Committee on Allergy Services offered by the British Society of Allergy and Clinical Immunology (BSACI) and draw your attention in particular to their concerns regarding the uncontrolled proliferation of unconventional allergy services. In my opinion these flourish because, at present, the NHS is seriously lacking in main stream, evidence-based allergy specialists and attendant facilities.

It would be unfortunate if the frequent conflation of allergy and intolerance, and the questionable science behind the commercially available tests for the latter, lessened the perceived significance of true allergy. Some commentators see claims of dietary intolerance as a modern manifestation of regarding nature as good or bad or an underlying fear that modern life is toxic. It is undeniable that if dietary and specialist allergy advice were more high-regarded and available in the UK then patients might feel that GPs are able to "understand their problems" and GPs might have clearer information on which to found recommendations rather than reassurance which may not help or the claim that "it is all in your mind".

Allergy has the potential to kill and allergies must be treated with respect. Allergies must have clinical assessment and management.

The picture is less clear for intolerances. It may be very unwise to restrict your own or a child's diet on the basis of scientifically-dubious tests and in the absence of a clinical assessment. There is some speculation that restriction might even contribute to later sensitivities for a child if there are no appropriately low-level challenges to the immune system. There seems to be little value in test results that are not grounded in science and may imply the need for dietary-restrictions or allergen-avoidance that may have such a significant impact on your well-being or that of a child.

Earlier related posts: Asthma and Food Allergies: Fashion or the New Form of Spiritual Re-Awakening?
Some Sticky Numbers and Comparisons for Food Allergy and Intolerance

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