Anaemia in patients diagnosed with paediatric-onset inflammatory bowel disease: A Danish nationwide cohort study.

OBJECTIVES: Anaemia impairs daily activities and quality of life in patients with paediatric-onset inflammatory bowel disease (PIBD). This study aimed to investigate the prevalence of anaemia at PIBD-diagnosis and the following 5 years. Furthermore, anaemia subtypes and the association between anaemia and disease activity were assessed over time. METHODS: Patients (6-17 years) diagnosed with PIBD between 2014 and 2022 were identified from Danish national health registers. Anaemia was defined according to the World Health Organization criteria. Anaemia subtypes (iron deficiency anaemia [IDA], anaemia of chronic disease [ACD], and IDA + ACD) were classified using guidelines by the European Society for Paediatric Gastroenterology, Hepatology, and Nutrition. PIBD disease activity was based on medication, surgeries, and hospitalisation. RESULTS: Of 1266 incident patients with PIBD, 660 (52%) were anaemic at diagnosis, decreasing to 25% in year 5. Moderate anaemia was most frequent at diagnosis and in the first year, while mild anaemia was more frequent in the following years. Of patients with anaemia at diagnosis, 237 were assigned a subtype; 25 (11%) presented with IDA, 44 (19%) with ACD, and 168 (71%) with IDA + ACD. Anaemia was associated with disease activity during the 5 years following PIBD-diagnosis with a peak association in year 4 (adjusted risk ratio: 2.3; 95% confidence interval [CI]: 1.8-3.0). CONCLUSIONS: Anaemia was common at PIBD-diagnosis and, although the prevalence decreased over time, especially mild anaemia, remained frequent. IDA + ACD was the most common subtype at diagnosis and disease activity was associated with anaemia.