Diagnostic Accuracy of Tissue Transglutaminase and Combined Assay of Tissue Transglutaminase and Deamidated Gliadin Peptide in Children with Coeliac Disease: A Cross-sectional Study

Introduction: Coeliac Disease (CD) is a systemic immune disorder caused by gluten in genetically susceptible individuals. A serological screening assay for CD has been designed to detect Immunoglobulin A (IgA) and IgG anti-tissue Transglutaminase (a-tTG) and IgA and IgG Deamidated Gliadin Peptide antibodies (a-DGP) simultaneously. The seronegative gap can be closed when these two antigens are combined on a single solid phase. This is primarily because untreated CD children who are negative for antibodies of one of the antigens may exhibit a positive result for the other. .Aim: To determine the diagnostic parameters {sensitivity, specificity, Positive Predictive Value (PPV), Negative Predictive Value (NPV)} of tTG-IgA and htTG-DGP (Coeliac fusion- a combination of IgA and IgG to human tTG and synthetic DGP) for the diagnosis of CD in clinically symptomatic children. Materials and Methods: This cross-sectional study was conducted at the Paediatric Outpatient Department (OPD) of Santokhba Durlabhji Memorial Hospital, Jaipur, Rajasthan, India from April 2023 to November 2023. The study population comprised 45 children (age >6 months and <18 years) showing clinical features of CD. Considering biopsy as the gold standard, the diagnostic parameters (sensitivity, specificity, PPV, NPV) of tTG-IgA and htTG-DGP were calculated with a 95% confidence interval for both tests. To determine the agreement between the two tests, Cohen's kappa was calculated. A p-value less than 0.05 was considered statistically significant. Results: Out of the study population, 23 (46%) CD patients were in the age group of 3-6 years, while 13 (26%) patients were in the age group of 6-9 years. A total of 24 (53.3%) CD patients were males, and 21 (46.7%) were females. Chronic diarrhoea was the most common clinical feature in 31 (62%) patients. Considering duodenal biopsy as the gold standard, the study results showed that the anti tTG-IgA antibody test had a sensitivity of 91.1%, specificity of 80%, PPV of 97.6, and NPV of 50%. In comparison, the htTG-DGP antibody test had a sensitivity of 95.6%, specificity of 100%, PPV of 100%, and NPV of 71.43%. Conclusion: Currently, tTG-IgA is considered the best CD screening test. However, the inclusion of DGP IgG could increase diagnostic sensitivity, and a Combined IgA/G-DGP/ tTG assay could be even better than tTG-IgA for the diagnosis of childhood CD.