Blood Tests for Foods
There are now several types of tests for foods, and often they are quite inexpensive. As I mentioned in the discussion of food allergy, there are different kinds of food allergy. The relationship of food allergy to other antibodies circulating in the bloodstream is less clear than the relationship to IgE. Most blood tests offered today look at specific antibodies circulating in the bloodstream that the body has produced in association with foods. These are primarily IgG antibodies, although most popular tests analyze both the IgE and IgG antibodies related to specific foods. The analysis is quantitative, and the levels of antibody are usually classified from 0 (no antibody) to 4+ (a lot). Analysis of both IgE and IgG antibodies to each food tested “covers more ground”.
There is an inborn problem with these types of tests. It is clear that we can produce antibodies to just about everything, and the more commonly we are exposed to things – whether we are allergic to them or not – the more likely we will produce antibodies at some level. The Big Question: how much antibody to we have to produce before we can be considered “allergic” to a substance? A little? A lot?
Well, there’s the rub. Some patients have symptoms from a food when they produce a little antibody (IgE, IgG or others) – or NO antibody, and some patients have symptoms only with a lot of antibody. And some patients have no symptoms yet they produce a LOT of antibodies to a food. So you run the analysis, but who’s who?
Most companies who offer these tests advise patients and physicians that patients should eliminate any foods to which they test positive (how positive varies with testing services) for some period of time, evaluate their symptoms, reintroduce the eliminated foods and try to determine whether the foods bother them in any way.
Generally speaking, patients who have any genetic predisposition to have food allergy or intolerance become allergic to the most common foods in their diet, and their favorite foods. Most Americans have foods that are present in their diet more than others, such as wheat and dairy. In fact, most Americans eat these foods every day. That’s why dairy and wheat allergy are so common, not to mention that these foods are more “potent” allergens than many other foods.
It is also true that people are more likely to produce antibodies to foods they commonly eat.
So you run a test like this, and dairy and wheat come up positive. This could be because: 1) the patient is allergic to them, or 2) the patient eats a lot of them, or 3) both. The patient who is not really allergic to these foods but has some antibodies to them because they eat them often will feel no better when he or she eliminates them and will say the test was false. The patient who is sensitized to these foods will feel better when they are eliminated, and will say the test was accurate.
The important point is that foods like wheat and dairy, because they are substantially allergenic in the first place and because Americans eat them so often, are the foods most commonly responsible for food sensitivity (not true IgE-mediated allergy) in our society. Since these two foods come up more often than most others as positive on food testing panels, they are commonly eliminated, and it’s common for patients to say the test “worked” because they feel better when these foods are eliminated. Was it the test that worked, or was it just playing the odds?
Needless to say, I don’t perform blood tests for foods, since there is far too much inaccuracy involved. As you can see, these types of tests might be accurate for some and not worth much at all for others. I generally use a trial (30 day) elimination diet to help our patients determine their food intolerances. This diet usually tells patients what foods they need to stop eating to feel well again. Of course, the problem is that many patients have become sensitized to many, many foods, and they are unable to eliminate them all. These patients usually do well on LDA immunotherapy.
We also use a type of testing called Provocation/Neutralization to test some of our patients for a limited number of foods. This method, since it may produce significant symptoms when positive foods are tested, often graphically tells patients what foods they need to eliminate!
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Santa Fe Center for Allergy and Environmental Medicine