I’ve written several times on the topic of food allergies and food intolerances, but was recently asked by a friend about some food allergy testing she had had done, and so I’ve decided to devote today’s entry to food allergy testing. This is a very large topic and one I’m sure I’ll return to many times in the future.
Let’s start with a brief clarification about food allergy testing. There are two types of testing commonly referred to as food allergy testing – one tests IgE reactions, the other tests IgG reactions. IgE reactions cause classic allergic reactions, with swelling, difficulty breathing, and other symptoms. These symptoms come on strongly, suddenly and with clear provocation. Two of the best known offenders in this category are peanuts and shellfish. IgG reactions are more complicated, can cause more varied and subtle complaints, and are harder to test. It’s this second category that I’d like to talk about today.
A lot of healthcare providers (NDs, MDs, and others) are starting to use IgG testing in their practices, and so many of my patients come in either having done the labs, or asking questions about the labs. Many docs swear by it, and indeed, I recently wrote an entry about a study that used food intolerance testing to gain positive clinical results for ADHD. In no way do I mean to discredit these docs’ experiences, but my experience has mixed, and I think there’s a very clear reason why.
Let’s start by talking about what qualities make up a good lab test. LDL Cholesterol is a great example to use in discussing this topic. (For those who want a refresher course on LDL Cholesterol, read this blog entry from a few weeks ago.)
The first quality of LDL Cholesterol that makes it a high quality lab test is the specificity of the substance being tested. The blood is full of protein, fat, minerals, and a variety of cells – there are literally thousands of compounds that one could test for using a blood sample. LDL Cholesterol, however, tests a very specific component of the blood – a lipoprotein of a certain size and density. Because no other substances are being included in the sample, the lab results are very consistent and reliable.
A good analogy can be drawn between lab testing and tuning a radio. I know that no one uses analog radios any more, but those of us old timers who remember having to turn a knob understand what I mean. A radio works by selecting a very specific frequency of radio transmission, and excluding all others. Being able to tune precisely to 100.7 allows us to hear only one station at a time, and to hear it clearly. If we were only able to tune to 101, we’d hear stations broadcasting at 100.7, 101.2, 101.5 and all the static in between. Tuning to 100.7 gives us music, tuning to 101 gives us noise.
The second quality that makes LDL Cholesterol a good lab test is that there are very clearly established normals. What this means is that a very large number of people had this lab test done on them, and those lab test results were then compared to clinical results to establish a clear understanding of how the lab values relate to the clinical results. As a result, I can now run LDL Cholesterol on a patient and be able to tell how likely or unlikely they are to suffer a negative outcome. The more times the lab is run, and the more that information in compared to clinical outcomes, the better able we are to interpret the results by matching them to their most likely clinical outcome.
So bearing that in mind, here are my experiences with IgG food testing. In a small number of cases, the results are very clear. When this happens, a person is non-reactive to virtually everything but a very few foods – sometimes it is a specific food, like eggs or potatoes, sometimes it is a group of foods, like citrus, beans or nightshades (potatoes, tomatoes, peppers, etc.). This is a best case scenario, and one that’s easy to work with. More commonly, however, I see results that indicate that the patient is mildly reactive to everything, with a few moderate elevations here and there of unrelated foods. This result is equivalent to tuning into several stations at the same time – it’s noise, and it’s hard to tell what’s going on. I think that this situation can be best explained because of problems the criteria I mentioned previously.
The first criterion is specificity. IgG testing, rather than testing for a reaction to a very specific molecule, or set of molecules, tests for a wide variety of compounds. The result is that a large number of reactions take place, not all of which may have a negative clinical outcome. Without going into a full discussion of the IgG immune reaction, it’s important to note that not every activation of the immune system results in symptoms. To create lab tests of better clinical value, IgG food intolerance testing will have to move towards a more narrowly defined set of substances being tested, substances which are more strongly linked with symptoms.
The second criterion, which I believe is equally important, is that an agreed-upon set of normals has not been established. As I stated before, not every activation of the immune system results in symptoms, and without a larger pool of data (both lab results and clinical outcomes), it is hard to interpret the results. It may be that a certain degree of reaction against a food may be totally normal, and not correlated with clinical symptoms. However, under current testing, that food shows up as reactive, and a person avoids it needlessly. I would hope that as time goes on, the bar is raised on immune reactions, so that minor, normal reactions are not counted as clinically significant.
To conclude, all lab tests have kinks that need to be worked out. Nowhere is this more true than in the immune system – many cancer markers, for example, have taken decades to prove their clinical use. Understanding food intolerance is difficult, and the technology is in its infancy. As time goes on, the method of testing and the interpretation of results will improve, but this is still some time off. The current problems with the testing are due to a less-than-sophisticated manner of testing reactions, and a poor ability to interpret results. In some cases, positive clinical outcomes have been observed, but before these tests gain widespread acceptance and show their true importance, improvements will need to take place.