may be entirely asymptomatic. Furthermore, although biomarkers of genetic susceptibility (e.g., presence of DQ2 and/or DQ8 HLA alleles) and gluten exposure [e.g., antibodies for gliadin (AGA), endomysial (EMA), and tissue transglutaminase (tTG)] have been defined for use in noninvasive diagnosis of individuals with celiac disease, these biomarkers have not been shown to correlate with disease severity nor to be useful in assessing daily responses to gluten exposures. Rather, evidence of intestinal mucosal inflammation is the gold standard biomarker for diagnosis of celiac disease and for assessement of disease severity. Intestinal mucosal inflammation may occur long before the development of clinical signs or a rise in antibody titers following a gluten challenge. Intestinal inflammation is assessed by intestinal biopsy, which is an invasive procedure, associated with false negatives (due to sampling error), and is impractical for frequent monitoring of disease activity or severity.
c. Foods of Concern. The foods of concern for individuals with, or susceptible to, celiac disease are the cereal grains that contain the storage proteins prolamin and glutelin (commonly referred to as glutens in wheat), including all varieties of wheat (e.g., durum, spelt, kamut), barley (where the storage proteins are called hordiens), rye (where the storage proteins are called secalins), and their cross-bred hybrids (such as triticale). The proportion of individuals with celiac disease that are also sensitive to the storage proteins in oats (avenins) has not been determined but is likely to be less than 1% (Kelly, 2005).
d. Methods of Analysis. The criteria used to evaluate the available methods of analysis for gluten in food are shown in Table IV-8 and are applied in Appendix 4. A number of commercial immunology-based ELISA test kits for the detection of gluten in foods are available, and one has been validated by AOAC (the Tepnel kit, validated at 160 ppm). One limitation of these kits is that they only detect prolamins. This is not likely to limit the detection of gluten in foods because in most cases prolamins and glutelin occur together. However, it may lead to an underestimate of the level of gluten present. Also, none of the test kits cross-reacts with protein extracts from oats, which limits their efficacy for the small portion of celiac patients who are also sensitive to oats. Test kits suitable for the detection of oat proteins should be developed. .
Table IV-8. Specific Criteria for Evaluating Gluten Analytical Methods
Criteria 1. Has the method been validated?
Comments Methods that have been validated (such as
by AOAC) are preferred. Alternatively, the sensitivity, precision, and reproducibility of the method should have been demonstrated in a peer-reviewed publication.
2. Is the method sufficiently sensitive?
The limit of detection and the limit of quantitation should be below the levels that appear to cause biological responses in most patients with celiac disease.
3. Are extraction methods available for
Different methods may be needed; each
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