Objective: The aim of this study was to evaluate performance of serum antibodies against deamidated gliadin peptides (a-DGPs) in detecting compliance with gluten-free diet (GFD) in children with celiac disease (CD).
Patients and methods: Serum samples were collected the same day of endoscopy in 95 children with CD and 106 controls. We preliminarily calculated the cutoff of a-DGP immunoglobulin A (IgA) and a-DGP IgA+G in our population by receiver operating characteristic (ROC) curves. Of 95 children with CD, 28 were studied during the first year after GFD introduction, with interview and serum collection every 3 months. In addition, serum samples were collected in 106 children with CD on GFD for more than 1 year (range 1-14). In both groups of children with CD on GFD, we compared a-DGP IgA and IgA+G performance in monitoring compliance with GFD with anti-tissue transglutaminase antibodies (anti-tTG) IgA and anti-gliadin antibody (AGA) IgA.
Results: The cutoff resulted in 13.1 arbitrary units (AU) for a-DGP IgA (sensitivity 87.4, 95% confidence interval [CI] 79%-92%, specificity 97.2, 95% CI 92%-99%) and 16.5 for a-DGP IgA+G (sensitivity 94.7, 95% CI 88%-98%, specificity 89.6, 95% CI 84%-95%). In the first year of GFD, at 6 to 8 months prevalence of positive a-DGPs was significantly higher in partially versus strictly compliant children, and at 9 to 12 months only prevalence of positive a-DGP IgA+G remained significantly higher. Moreover, at 9 to 12 months sensitivity to detect transgressions to GFD was 44% for a-DGP IgA and 100% for a-DGP IgA+G (P = 0.03). In the 106 children on GFD for more than 1 year, sensitivity to detect transgressions to GFD was 60% for a-DGP IgA and 76% for a-DGP IgA+G. Anti-tTG IgA and AGA IgA sensitivity was much lower (24% and 4%, respectively). The 4 tests showed comparable high specificity.
Conclusions: Both a-DGPs showed higher sensitivity than anti-tTG IgA and AGA IgA in monitoring compliance with GFD, but a-DGP IgA+G seemed to perform better. a-DGPs did not outperform anti-tTG IgA for CD screening.