Frequency of follow-up testing for tissue transglutaminase antibodies after initial positivity among children: An analysis of real-world data from a population-based cohort in Canada

Abstract Background Tissue transglutaminase antibodies (tTG-IgA) are the primary tool for celiac disease (CeD) screening, can be incorporated into a formal diagnosis of CeD without the need for biopsy-confirmation, and are recommended for subsequent monitoring of disease status. However, it remains understudied how frequently children are further tested after an initial positive result. Methods Administrative data from Alberta, Canada were utilized to identify children with their first positive tTG-IgA result between 2016 and 2023. Children were stratified according to baseline result: low (1.0-2.9× the upper limit of normal [ULN]), medium (3.0-9.9× the ULN), and high (≥10× the ULN). Mean cumulative functions were estimated to determine the average number of repeated tTG-IgA tests across time. Further differences were evaluated by sex, age, urban-rural status, and socioeconomic status. Results Among 4405 children with incident CeD autoimmunity, almost half (49.1%) had high baseline values at index positivity. These children also had the most overall and positive follow-up tests, on average. For example, within 5 years, those with baseline tTG-IgA ≥10× the ULN had, on average, 3.7 overall (95% CI, 3.6-3.9) and 2.5 positive (95% CI, 2.4-2.6) repeat tests, respectively, compared to 2.1 overall (95% CI, 2.0-2.2) and 0.8 positive (95% CI, 0.7-0.8) among those with 1.0-2.9× the ULN. Significant differences were also present across the urban-rural spectrum and the socioeconomic gradient (eg, highest in metropolitan centres). Conclusion These findings showcase notable variation in follow-up tTG-IgA testing among children with incident CeD autoimmunity in Alberta, Canada.