B-095 Concordance Between Anti-TG2 IgG and Anti-DGP IgG in IgA-Deficient Patients and Its Relationship with Age in Celiac Disease Diagnosis

Abstract Background Celiac disease (CD) is an autoimmune disorder triggered by gluten ingestion in genetically predisposed individuals. While serological testing is essential for diagnosis, there is no consensus on the optimal IgG-based markers for patients with total IgA deficiency. Additionally, the influence of factors such as age on these markers has not been thoroughly studied. Anti-tissue transglutaminase IgG (anti-TG2 IgG) and anti-deamidated gliadin peptide IgG (anti-DGP IgG) are commonly used in IgA-deficient patients, but their diagnostic performance and agreement remain uncertain. This study evaluates the concordance between anti-TG2 IgG and anti-DGP IgG and explores whether antibody positivity is influenced by patient age. Methods A total of 510 IgA-deficient patients were selected using Alinity c analyzers and classified into three age groups: 0-6 years (IgA <30 mg/dL), 7-18 years (IgA <50 mg/dL), and >19 years (IgA <70 mg/dL). Patients with anti-TG2 IgG and anti-DGP IgG results were identified using the BIWER NEOS database. Anti-TG2 IgG and anti-DGP IgG were analyzed using the Phadia™ 250 instrument from Thermo Fisher. Statistical analysis was performed using R Studio (version 4.4.0). Concordance between anti-TG2 IgG and anti-DGP IgG was assessed using Cohen’s Kappa coefficient and McNemar’s test. The effect of age on antibody positivity was analyzed using frequency tables, Chi-square tests, and logistic regression. Results The Cohen’s Kappa coefficient was 0, indicating no agreement between the two tests. McNemar’s test showed significant differences between them (p < 0.001), suggesting that they are not equivalent in detecting positivity. Age significantly influenced antibody positivity. Patients aged 7-18 years were more likely to test positive for anti-TG2 IgG, while patients older than 19 years were less likely to test positive for anti-DGP IgG. Conclusion Anti-TG2 IgG and anti-DGP IgG are not interchangeable tests in IgA-deficient patients. Age influences antibody positivity and should be considered when interpreting serological results. A combined approach is recommended to improve diagnostic accuracy in this patient group.