Cross-posted from Startled Disbelief.

A physician of my acquaintance recently brought this article to my attention. Written by Elaine Chin, a Toronto GP “with a holistic approach to health and wellness management”, it responds to a Globe and Mail article entitled “Tests for food allergies, sensitivities a ‘waste of money,’ doctor says”.

The Globe and Mail article is a good one, and I recommend that you read it, but I’ll summarize it for you here: Naturopaths and other “alternative” medical practitioners are sending their patients to be tested for immunoglobulin G, and suggesting extremely restricted diets based on the results of these tests. But according to allergist Dr. Elana Lavine, these practitioners haven’t established that IgG is indicative of food allergy or sensitivity of any sort: a positive test may be indicative of nothing more than repeated exposure to the food in question, which may mean that your favourite foods are more likely to find themselves on your stomach’s No Fly list.

My wife, who is a dietitian, has been seeing increasing numbers of patients come in with IgG panels, often showing “sensitivities” to just about every dietary staple. She also noted that at least one of the labs that sells IgG testing to the public describes immunoglobulin G as a “cell”, which is a disturbingly elementary error: immunoglobulins are proteins. For more background on IgG testing, I recommend this article by Scott Gavura of Science-Based Pharmacy.

But back to Dr. Chin, who was evidently unimpressed with the Globe and Mail article. On her blog, she writes:

Many of my professional colleagues have a contrasting position. Dr. Shelley Burns (a naturopathic doctor) and I use food testing to detect allergies, intolerances, sensitivities in our practice. We believe that such testing should be done under the supervision of professionals who understand the appropriate use of and know how to interpret the report. As well, the results are critically dependent on the source of lab testing. Only 3 labs in North America have been shown to have reliable and reproducible results – one of them is Rocky Mountain Analytical and their lab partner, US Biotek.

Dr. Chin works with a naturopath. I see.

I have along with Dr. Burns completed more than 100 Food IgG, IgE, and IgA tests in our practices for at least 5 years. I’m not at all certain that Dr. Lavine has worked with these tests and yet she is weighing in.

That’s right: Dr. Lavine, an allergy specialist, may have the necessary medical expertise, but does she have the appropriate personal experience? I think not!

I would also like to note that IgG, IgE, and IgA tests are not at all the same thing, and lumping them all together like that (especially when the article Dr. Chin is discussing was critical of only IgG testing) is indicative of sloppiness unbecoming a physician. Immunoglobulin E is closely associated with type I hypersensitivity (allergy), while immunoglobulin A has been linked to celiac disease.

By contrast, here’s what the American Academy of Allergy, Asthma and Immunology has to say about IgG testing: “IgG and IgG subclass antibody tests for food allergy do not have clinical relevance, are not validated, lack sufficient quality control, and should not be performed.”

The Australasian Society of Clinical Immunology and Allergy adds:

There is no credible evidence that measuring IgG antibodies is useful for diagnosing food allergy or intolerance, nor that IgG antibodies cause symptoms. In fact, IgG antibodies reflect exposure to allergen but not the presence of disease. 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. Despite studies showing the uselessness of this technique, it continues to be promoted in the community, even for diagnosing disorders for which no evidence of immune system involvement exists. [Emphasis added.]

Back to Chin:

I would be willing at any time to challenge my colleague Dr. Lavine as to our experience with a series of case studies where the testing results have in fact made a difference and reduced the chronic symptoms of migraines, irritable bowel syndrome and asthma.

Case studies to demonstrate efficacy? Really? You wouldn’t want to, I don’t know, use any sort of controls or blinding or anything?

The first two cases to be reviewed will begin with my son and me.

You have got to be kidding. Remind me again: When conducting medical research, are we trying to maximize researcher bias, or eliminate it? Because I’ve lost all confidence that Dr. Chin even knows what bias is.

And then, there are dozens of my clients and their children whose lives have improved as a result of their testing and subsequent appropriate dietary changes.

Post hoc ergo propter hoc. It’s a good thing that there are no well-documented medical effects that may cause inert interventions to be confused for effective ones.

In fact, what is a waste of money are tons and tons of imaging tests which do not diagnose the cause of irritable bowel, the chronic use of steroids medications for unknown triggers for asthma (creating issues such as bone thinning), and loss of work productivity hours due to migraines. And here is my warning to my physician colleagues. Before you comment in our medical journal, take the time to use the test before providing a professional opinion. Do your homework and due diligence as a scientist. I have done so.

Sure. Because “due diligence” means trying the test for yourself, rather than reviewing the medical literature and the best available scientific evidence. I’m honestly surprised that Dr. Chin didn’t make the “you’re just closed minded” gambit.

This article is almost a parody of itself.

There are legitimate allergies (and other hypersensitivities) that may require extremely restricted diets, and for those experiencing chronic symptoms of unknown origin it can be very heartening to think that they may have found the cause. But don’t waste hundreds of dollars on these tests and turn your diet on its head until IgG proponents have demonstrated that the results of these tests are medically useful.

Addendum: The fine folks at Bad Science Watch have pointed out a few other links of note.

First, the British Dietetic Association does not recommend IgG tests for food intolerance, based on the dearth of evidence:

This blood test looks at IgG antibodies present in the blood. It’s claimed that an increase in IgG to a certain food indicates an intolerance to that food. At present there is no convincing evidence to support this test, and it’s not recommended as a diagnostic tool.

Second, you can find an in-depth discussion of food intolerance (and IgG in specific) in the January 2008 issue of Today’s Dietitian.