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.

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.