Evaluating the clinical relevance of food sensitivity tests: a single-subject experiment

Alternative Medicine Review, June, 2004 by Patricia M. Herman, Lisa M. Drost

Abstract

A number of tests are available to identify food sensitivities. This article presents an analysis of the diagnostic value of nine different food sensitivity tests run concurrently on a healthy 33-year-old female with a previous diagnosis of environmental allergies. This case study evaluated conventional allergy tests (skin prick and serum IgE), tests of other immune-mediated reactions (serum IgG and salivary IgA), and tests that claim to measure the energetic reaction of the whole person to particular foods (kinesiology, Vega, and Carroll testing). The results of an elimination/challenge test were used as indicators of true food reactions in order to calculate the sensitivity, specificity, and positive predictive value (PPV) of each test. In a separate evaluation, the variability of results across the four tests measuring IgG was determined. Results show several tests (one of the two serum tests of IgG alone, both serum tests of IgE and IgG, skin prick testing, and Carroll testing) may have very high (100%) specificity and PPV when test results are compared to the results of an elimination/challenge test. Sensitivity, however, is low across tests (50-60 percent), likely because different tests measure different mechanisms of food reactions and because food sensitivities can be the result of a number of different mechanisms. Very little consistency was found among the results of the four tests measuring IgG--79-83 percent disagreement. This study shows a number of tests may be useful in identifying foods to which a patient is reactive; however, no one test is likely to identify all reactive foods.

Introduction

This article presents the results of a set of nine different food sensitivity tests run concurrently on a healthy 33-year-old female with a previous diagnosis of environmental allergies. This "subject" (one of the authors) underwent the series of tests to identify foods to which she was sensitive and to determine the diagnostic value of the various types of tests available. This paper presents the results of the latter.

In this case analysis, the term "food sensitivity" includes fill types of adverse reactions to food. In general, adverse food reactions can be divided into two groups: (1) those proven to be immunological in nature and thus are hypersensitivity reactions--mostly IgE-mediated (food allergies): and (2) those not proven to be immunologic in nature (food intolerances). (1)

While the actual prevalence of adverse food reactions is unknown, a consumer survey has indicated one-third of American households believe that at least one family member has adverse food reactions. (1) Estimates of the prevalence of food allergies range from 1-2 percent of the adult population to 4-8 percent of the pediatric population. (1,2) Prevalence estimates of one common type of food intolerance, lactose intolerance, range from two percent for those of Northern European descent to nearly 100 percent in adult Asians and Native Americans. (3)

There are a number of diagnostic tests available to identify food sensitivities. The "gold standard" for diagnosis of food sensitivity is the double-blind, placebo-controlled, oral food challenge. It is simple, but time consuming, and is usually administered only after other tests have indicated suspect foods. Conventional allergists focus on the immune system's response to a food or other allergen through IgE-mediated hypersensitivity reactions. These practitioners tend to use either skin or serum tests. (1) In the skin prick test, a minute quantity of a suspected allergen is injected into the epidermis. Significant erythema or a wheal and erythema indicate a positive reaction. Serum tests include those using radioallergosorbent test (RAST) or enzyme-linked immunosorbent assay (ELISA) techniques. A high level of circulating IgE specific to a particular food or other allergen indicates a positive result.

A number of serum tests are available that measure circulating IgG specific to particular foods or other antigens. These tests also measure an immune system response, but the IgG response to foods is not as well understood. (1) Similarly, salivary tests of secretory IgA specific to particular allergens are available. Again, the secretory IgA response to specific foods is not well understood. (4)

Other diagnostic tests look at non-immune-mediated reactions to food. These approaches are not generally recognized by conventional medicine and are believed to measure the energetic reaction of the whole person to a particular food. Included in this category are kinesiology (which uses loss in muscle strength as an indicator of food sensitivity), Vega testing (which uses a machine to measure electromagnetic pulses through the body), and Carroll testing (which measures intolerance to a food by running an electric current through a small sample of the subject's blood).

The purpose of this case analysis is to evaluate the diagnostic value of nine different food sensitivity tests, including commonly used conventional allergy tests, as well as other immune-mediated reaction tests and tests that measure the reaction of the whole person to particular foods.