Background: It is important to have methods for evaluating dietary compliance in patients with celiac disease (CD). Determination of fecal gluten immunogenic peptides (GIPs) was recently proposed as a method of detecting gluten intake. The aim of this study was to evaluate whether determination of GIPs can be used as an indicator of compliance with a gluten-free diet (GFD).
Methods: Twenty-five persons with CD on a gluten-free diet for at least one year were enrolled in the study. Compliance with the diet was assessed by the Biagi questionnaire, evaluation of symptoms and assay of IgA anti-tissue transglutaminase antibodies (IgA anti-tTG). GIPs were determined by iVYLISA GIP-S test (Biomedal S.L., Seville, Spain) on an automated Chorus analyzer (DIESSE Diagnostica Senese, Siena, Italy), after extraction of fecal samples by the method developed by DIESSE.
Results: Four patients tested positive for GIPs (GIP+), two of whom complied strictly with the gluten-free diet according to the Biagi questionnaire. None of the four GIP-positive patients manifested symptoms. IgA anti-tTG was significantly higher in GIP+ than in GIP- subjects.
Conclusions: Assay of fecal GIPs identified more patients who were not complying with the diet than the Biagi questionnaire or evaluation of symptoms. The anti-tTG and GIP results agreed perfectly; however, since anti-tTG antibodies remain high for longer and are not a completely reliable marker of GFD intake, detection of fecal GIPs offers a direct, objective, quantitative assessment of exposure, even occasional, to gluten and could be used to check dietary compliance.