Background: Celiac disease is frequently associated with iron deficiency without anemia (i.e., low ferritin, normal hemoglobin) due to compromised iron absorption. While ferritin levels of individuals with deficiency at diagnosis should normalize following initiation of a gluten-free diet, timing is variable and may not reach optimal thresholds in all individuals.
Methods: We conducted a population-based retrospective cohort study of all individuals in Alberta, Canada, who tested newly positive for tissue transglutaminase (tTG-IgA) between April 2015 and March 2025. We linked these individuals to ferritin tests occurring before and after index positivity. Cox proportional hazards regression evaluated time to ferritin normalization, and generalized estimating equations quantified changes in ferritin concentration over time (adjusted for age, sex, tTG-IgA level at index positivity, material deprivation, and Charlson comorbidity score).
Results: Among 13,513 patients with celiac autoimmunity, most (89.7%) were tested for ferritin at some point during the study period. Among those with ferritin results at baseline tTG-IgA positivity (±5 days), 30.0% of patients had ferritin deficiency and 63.0% had ferritin ≤50µg/L. Females, adults, and individuals living in the most materially deprived areas were more likely to be tested and have deficient results, respectively (p<0.001). Median time to normalization was roughly two years, with high baseline tTG-IgA resulting in significantly faster normalization (HR = 1.34; 95% CI = 1.15, 1.56) despite lower ferritin levels overall (−41.8 µg/L; 95% CI = −60.9, −22.8). Time after index tTG-IgA positivity was associated with higher ferritin levels overall (+14.5 µg/L; 95% CI = +3.56, +25.4). Approximately 13.0% of individuals who had ferritin normalize after index tTG-IgA positivity experienced recurrent deficiency at a later follow-up measurement.
Discussion: Given variation in ferritin levels, probability of testing, and time to normalization, there may be a need for more frequent follow-up testing of ferritin in certain populations with celiac disease.