Commercial assays to assess gluten content of gluten-free foods: why they are not created equal.

A standardized method of analysis is needed to quantitatively determine the gluten content of food and provide the basis for enforcing regulations regarding use of the term gluten-free in food labeling. People with celiac disease should feel confident that foods labeled "gluten-free" have been assessed for gluten using the same "best available" methodology. The Association of Analytical Communities and the Codex Alimentarius Commission endorse different methods. Both are used by manufacturers in the United States to determine the gluten-free status of food. The sandwich omega-gliadin enzyme-linked immunosorbent assay (ELISA) is the official method of the Association of Analytical Communities. It is able to quantify native and heated gluten. It is unable to accurately detect and quantify barley prolamins, can over- or underestimate gluten content, and cannot accurately quantify hydrolyzed gluten. The sandwich R5 ELISA was endorsed by Codex for gluten determination. It is able to quantify native and heated gluten. One criticism is that it overestimates barley hordein. It also is unable to accurately quantify hydrolyzed gluten. Foods that can be reliably assessed for gluten using a validated commercially available ELISA are those contaminated with native and heated proteins from wheat, barley, and rye. The degree of confidence that can be placed in a manufacturer's assertion that a product is gluten-free is based on the assay used to determine the gluten content and the specific food analyzed.