Diagnostic Tests for Adverse Food Reactions

Before reading this article, it’s probably a good idea to have read my article on food sensitivities and immune reactions. Then take a look at the article below, which is a brief overview of some test options for finding adverse food reactions.

An accurate adverse-food-reaction test is both sensitive and specific. An insensitive test will miss problematic foods; that is, it will give false negatives. A test with poor specificity will identify some foods as problematic, when, in fact, they are not; these are false positives. Also, a test should be reliable; that is, it gives at least 90% consistent results when performing the same test twice on a split sample of blood.

The most accurate food-hypersensitivity test is oral challenge. This is typically done in hospital (due to the risk of anaphylaxis) and is time consuming, tedious, and difficult. The patient eats one and only one food per day. Results are then observed. Over time (a great deal of time!) it becomes clear which foods cause problems and which do not.

The challenge with lab tests for food sensitivities is that there are many (over 100) immune-system mediator chemicals that can lead to illness and discomfort. These mediators include histamine (which causes inflammation and smooth-muscle contraction), cytokines (which can increase or dampen immune reactions), and prostaglandins (which can cause inflammation and pain-receptor activation).

Mediators are found in immune cells and are synthesized in circulation. The list of immune cells is long, and each type of immune cell has a different profile of mediators. Further complicating the diagnostic process is that different hypersensitivity reactions can involve many different immune cells. This means that one can’t assume which cell(s) are involved in the reaction.

Immune mechanisms cause mediator release. Mechanisms include antibodies (IgE, IgG, IgM), complement (C3, C4), and cellular reactions (T-cells).

True allergic reactions primarily involve mast cells, an IgE mechanism, and the release of histamine and other mediators. One test for these IgE reactions is skin testing. Skin pricks/scratches deliver specific antigens (for example, beef, egg, fish, etc) directly into the skin and the swelling/redness response (similar to a mosquito bite) is analyzed. This test is excellent for inhaled allergens (dust, pollen) but poor for food allergens, with about a 40% accuracy. It is useless for food sensitivities, which use a non-IgE pathway of the immune system.

Other food-allergy (not food-sensitivity) tests quantify the amount of IgE present (via RAST or ELISA methodologies). These tests are about 60% accurate for food allergies.

There are some other less-frequently-used food-allergy (IgE) tests known as BHRT and LHRT. These tests compare measurements of histamine in control versus antigen-challenged samples. Like the RAST test, the accuracy is about 60% for food allergies, but the blood sample has a shorter viable life span.

None of the preceding blood tests address food sensitivities (type-3 and -4 immune reactions); the preceding blood tests only address type-1 reactions. Food sensitivity testing presents a puzzle because one must test for reactive foods and chemicals, but the immune responses involve many mediators, cells, and mechanisms.

Some options:

IgG ELISA testing is accurate for measuring IgG but there are several problems. IgG in some cases is a protective antibody, not harmful. The test only measures IgG, which is only involved in some, not all immune reactions. It’s not a useful test for irritable-bowel syndrome (IBS) or migraine, and it can’t test for food chemicals or additives.

ALCAT testing measures changes in white-blood-cell size after antigen exposure. This was a promising test but which has poor split-sample reproducibility and can’t measure lymphocyte (T-cells, NK cells) reactions.

LRA by ELISA/ACT testing had no published studies on reliability or valididty, no support anywhere in medical literature, and the test ignores the importance of granulocytes and mediator release.

Mediator-release test (MRT) measures the changes in ratios of liquids to solids after whole-blood exposure to antigens. This test can’t identify IgE-mediated reactions (true allergic reactions), and it must be done within 32 to 36 hours of taking the blood sample, which is why part of the blood-draw process includes FedEx overnight transport to the lab.

The MRT does offer excellent accuracy for sensitivity reactions (all non-IgE-mediated reactions to food), with a 94.5% sensitivity and a 91.7% specificity. Its reliability of split-sample comparisons is above 90%. It provides endpoint measurements (outcomes of all non-IgE reactions). It can measure both food and chemical reactivity. The test also quantifies the level of reaction, which greatly helps in diet design.

The MRT is the blood test that is the foundation of the LEAP (lifestyle eating and performance) protocol.

It is important to recognize that all food-sensitivity testing (whether optimally valid and reliable or not) provides a limited list of safe foods/chemicals and triggering foods/chemicals. Most persons tend to view the results as a list of foods  to avoid — end of story. However, that is not the end of the story. Because there are thousands of foods and food chemicals that we might consume, any sensitivity test is just a window to that universe. So these tests provide not only a foods-to-be-avoided list, but also a safe-foods list. It is the latter, the safe-foods list, that the dietitian and client use as a starting point in a process to eventually introduce non-tested foods and evaluate for sensitivities to those.

Author: Doug Hansford

Registered Dietitian/Nutritionist — trained in university and hospital; certified by the Commission on Dietetic Registration (RDN credential) and by Oxford Biomedical Laboratories (CLT credential). Member of the Academy of Nutrition and Dietetics. Specializing in food sensitivities treating irritable bowel syndrome (IBS), migrane, fibromyalgia, and other conditions related to food sensitivities, which can include asthma, eczema, heartburn/GERD, arthritis, joint pain, chronic fatigue, chronic sinusitis, skin eruptions, and autism/ADD.

Also a former certified personal trainer and part-time lecturer in the department of nutrition and food science at a major research university.