Thursday, July 06, 2006

Food Allergy And Intolerance Testing: Makes Me See Red

Sign text reads: Peanuts and peanut dust everywhereFood allergy and intolerance are sometimes derided as 'populist illnesses'. However, parents are desperate to do something for their ill or distressed children. If they suspect an allergy or intolerance, they have so much difficulty in finding appropriate testing on the NHS that many of them consider mail-order testing that sounds plausibly scientific. The problem is that most of these food allergy and intolerance tests make me see red - I know so many people who have paid out hundreds of pounds for meaningless results.

On an earlier version of his site, Dr. Adrian Morris provided a good summary of the value or scientific basis of these tests.
An Allergy Test should accurately and reliably identify one or more agents to which the patient reacts on each exposure. These allergens must be the cause of the patient’s immune-mediated allergic symptoms. This reaction need not necessarily be IgE mediated, but may involve a T-cell Delayed hypersensitivity reaction or direct Histamine release from Mast Cells and Basophils. The test should be reproducible and identify the implicated allergen on each occasion the test is done. The allergy should be specific to that allergen with minimal false positive test results (when the test is positive in someone with no allergy), or false negative test results (where the test is negative in a person who is known to be allergic to that allergen).
He also reserved his judgement about the value of the YorkTests:
IgG4 antibodies may play a role in food intolerance or IBS, and are currently being evaluated by Allergy UK in conjunction with York Laboratories and further studies will be published shortly.
Visiting the YorkTest site, you will see reference to 1 published study, and the results were not striking. But, I suppose that the rest of the 'evidence' is still in the process of collation and review.

Dr. Morris no longer refers explicitly to the YorkTests in his overview of controversial aspects of allergy tests and testing, but he does quote the abstract of a paper by Wuthrich on Unproven Techniques in Allergy Diagnosis:
Although some papers suggest a possible pathogenetic role of IgG, IgG4 antibody, no correlation was found between the outcome of DBPCFC and the levels of either food-specific IgG or IgG4, nor was any difference seen between patients and controls. The levels of these and other food-specific immunoglobulins of non-IgE isotype reflect the intake of food in the individual and may thus be a normal and harmless finding. The so-called 'Food Allergy Profile' with simultaneous IgE and IgG determination against more than 100 foodstuffs is neither economical nor useful for diagnosis.
Somewhere, I have seen the caution that if you have been avoiding a foodstuff for some time before the testing, there may not be any antibodies/antigens present and your results may therefore contain a false negative. You are counselled, however, that you should not therefore decide to deliberately eat a food that you suspect causes a reaction, just for the benefit of the test.

I'll leave aside some of the issues that really annoy me. But, if a child's parents have been modifying the diet to exclude suspect foods, won't the results be open to the interpretation that they are (very expensive) false negative results? Parents' money is their business: how they feed their child is their business but I would wish that their decisions were not based on a test that has an unproven scientific basis.

I recommend reading an article by Sheryl Miller, IgG Food Allergy Testing by ELISA/EIA What Do They Really Tell Us? I have some criticisms of the article and the source but it does report a useful evaluation of inter-lab and intra-lab reliability, the test subject:
tested reactive in 76% of Lab A’s test (73 positive/96 foods), in 29% (28 positive/95 foods) of Lab B’s test, and reactive in 22% (22 positive/102 foods) of Lab C’s test.
Miller also raises useful questions as to the reliability of the test strata and the challenge substances. Beyer and Teuber offer this useful summary:
The skin prick test and measurement of specific IgE antibodies to food extracts, individual allergens or allergenic peptides are helpful in the diagnostic approach. Food-specific IgG continues to be an unproven or experimental test. The other alternative and complementary techniques have no proven benefit and may endanger patients via misdiagnosis.
If you really think that allergy testing would help your child, ask your doctor if it is possible to have a referral to an appropriate clinic if they do not offer the services at your surgery. It may be very unwise to restrict your own or a child's diet on the basis of scientifically-dubious tests. 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-restrications or allergen-avoidance that may have such a significant impact on your well-being or that of a child.

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13 Comments:

Blogger purple_kangaroo said...

Strict avoidance of any allergen is so difficult and frustrating, and avoiding multiple allergens is even worse. Sometimes I think about going back to school after my kids are grown and becoming either an allergist or an allergy researcher, just to try to speed up the finding of better testing and solutions.

You said, "Restriction might even contribute to later sensitivities for a child if there are no appropriately low-level challenges to the immune system."

Unecessarily severe restriction of the diet could also cause problems by sensitizing an atopic child to become allergic one of the "safe" foods because they're eating the same foods all the time and not getting enough variety, couldn't it?

What do you think of avoiding all common allergens for the first year or more of a child's life to minimize the likelihood of developing allergies to them?

We're seeing a new allergist this week, and I really hope he will be willing to help us challenge apples, which Baby E tested positive to but we're not sure she's really allergic to. It would be fantastic to be able to add apples back into our diet.

11:55 pm  
Blogger Shinga said...

I agree about the sensitization point, Purple Kangaroo. I met a young child who had been OK with soya when it was consumed in small quantities. However, her parents restricted dairy in her diet and started giving her more soya forms. The little one developed OAS and had a wretched time with soya. She became sensitized to even tiny amounts.

There have been a number of clinical studies about restricting exposure to allergens in early years. There hasn't been any evidence of a protective effect. As ever, some of the findings even point towards greater vulnerability for disorders such as eczema.

Good luck with the allergist.

Regards - Shinga

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