Unreliability of IgE/IgG4 antibody testing as a diagnostic tool in food intolerance

Background Some clinicians link chronic disease in certain patients to ‘food intolerance’. This is currently diagnosed by exclusion dieting, a time-consuming and tedious technique. It has been claimed that IgE/IgG4 antibody testing is a rapid and valid method of determining food intolerance. Objective To determine the test/retest reliability of IgE/IgG4 antibody testing as a diagnostic tool. Methods Blinded testing of duplicate blood samples from nine patients with suspected food intolerance was undertaken by tertiary referral centre using the services of a commercial laboratory. The proportions of consistent and inconsistent results for tests of 95 different foods were analysed. Results Test/retest reliability was low. Even though the study method systematically over-estimated kappa, this value never exceeded 0.51, regardless of the statistical model used. All but one patient had a greater number of inconsistent results than had been prespecified as an unacceptable level of disagreement. In one case, 50 out of 95 test results were inconsistent on retest. Conclusions We found no evidence that IgE/IgG4 antibody testing as performed by this laboratory is a reliable diagnostic tool.