Trip Answers

Question answered:23/08/07 Warning! this question is over two years old.

The Royal College of Pathologists guide on allergy and allergy tests distinguishes between food intolerances and food allergies:

 

“‘Allergy’ involves the immune system and tends to occur on each and every exposure. Many allergy tests measure specific immune factors triggered by allergies.

 

‘Intolerance’ does not involve the immune system and so allergy tests will be useless. Sometimes the intolerance is scientifically understood (an enzyme deficiency and specific forms of food intolerance, for example), but often the explanation is not clear. ..” [1]

 

An e-Medicine article on food allergies gives the following information:

 

“Adverse food reactions can be broadly classified into 2 categories. The first category consists of immunologically-mediated adverse reactions to foods; these reactions are unrelated to any physiologic effect of the food or food additive. These reactions include disorders mediated by immunoglobulin E (IgE) antibodies (eg, IgE-mediated reaction to peanuts), which begin during or soon after exposure to the food, and others resulting from non–IgE-mediated mechanisms (eg, non–IgE-mediated reactions such as protein-induced enterocolitis syndrome), which generally take several hours to evolve. 

 

The second category is food intolerance. These reactions include any adverse physiologic response to a food or food additive that is not immunologically mediated (eg, lactose intolerance, bacterial food poisoning).” [2]

 

The Royal College of Pathologists guideline, referred to above, discusses the range of allergy tests available. It states that, “IgG-based” allergy tests are best avoided. IgG antibodies to foods, for example, are found commonly, even in healthy non-allergy individuals. For example, IgG antibody to wheat gluten is found in 10% of normal healthy people who eat wheat regularly without problem.”

 

In addition, it considers the value of commercial allergy tests:

 

“Commercial allergy tests (from supermarkets, high street shops or by post)
These are not recommended. Some forms of postal testing (requiring hair or urine or other unorthodox samples) are of dubious scientific value. NHS-based laboratories and clinics are expected to perform to minimum standards and in so doing earn an accreditation certificate. Many commercial establishments operate to poorer quality standards.
Failure to limit test selection and failure to interprete test results against the details of the patient’s symptoms and medical history leads to confusion and error and is strongly discouraged.” [1]

 

In its guideline on allergy, the Royal College of Physicians considers the use of IgG in Table 9.2 entitled, ‘Alternative tests of no proven value in allergy diagnosis’:

 

Rationale
“Specific IgG antibodies are suggested to identify food sensitive individuals. The role of these IgG antibodies in the pathogenesis of these conditions is not established.

 

Indication
“No validated use. Used for possible food related to chronic disease.”

 

Interpretations/limitations:
Dietary advice including food avoidance and food rotation is made depending on result. However, these antibodies are present in normal healthy subjects. Randomised controlled trials to establish the value of IgG antibodies in food sensitivity are required.”

 

Please note Table 9.1 lists the tests used in allergy diagnosis and gives the rationale, indications and limitations associated with each.

References
1. Royal College of Pathologists. Allergy and allergy tests: a guide for patients and relatives. 2002 (revised 2004 and 2005). (http://www.rcpath.org/resources/pdf/allergy_doc.pdf)
2. Atkins D Food allergies. E-Medicine. June 2006. (http://www.emedicine.com/med/topic806.htm)
3. Royal College of Physicians. Allergy: the unmet need: a blueprint for better patient care. June 2003. (http://www.bsaci.org/open/pdf/allergy_the_unmet_need.pdf).

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