Abstract Background Anaemia is one of the most frequent complications in patients with paediatric-onset inflammatory bowel disease (PIBD), impairing patients’ daily activities and quality of life. This study aimed to investigate the prevalence of anaemia at diagnosis and in the following five years. Furthermore, we aimed to identify the type of anaemia at diagnosis and to assess an association between disease activity and anaemia for the first five years of follow-up. Methods Patients diagnosed with PIBD (6 – 17 years) between 2014 and 2022 were identified from nationwide registers using a previously validated algorithm. Biochemical data was retrieved from the Clinical Laboratory Information Register. Anaemia was defined according to World’s Health Organisation (WHO)1. For each year, the lowest haemoglobin value was used to determine a yearly period prevalence of anaemia. Anaemia subtypes (iron deficiency anaemia IDA, anaemia of chronic disease ACD, and IDA + ACD) were classifed according to the ulcerative colitis guidelines by ESPGHAN2 and based on the levels of mean corpuscular volume, transferrin saturation, ferritin, erythrocyte sedimentation rate, and C-reactive protein. Relative risks (RR) with 95% confidence intervals (CI) were calculated to compare the risk of anaemia between patients’ characteristics. Disease activity (start or switch of medication, IBD-related surgery, and hospitalisation) was assessed the following 5 years after diagnosis (diagnostic colonoscopy). Results Of 1266 included patients with PIBD, 660 (52.1%) were anaemic at diagnosis. The period prevalence of anaemia and anaemia severity at diagnosis and during the first five years are presented in Figure 1. Of patients with anaemia at diagnosis,122 were assigned a subtype. Seventy-eight (64%) presented with IDA+ACD, 22 (18%) with exclusive IDA and 22 (18%) with exclusive ACD. At diagnosis, girls had a higher risk of anaemia than boys (RR: 1.2, 95%CI: 1.1-1.3), as did patients with Crohn’s disease compared to ulcerative colitis (RR: 1.2, 95%CI: 1.1-1.3). Anaemia was associated with disease activity (Figure 2). Conclusion Anaemia was common at the time of diagnosis of PIBD and during the first year, but decreased over time. The combination of IDA and ACD was the most common subtype of anaemia at diagnosis. IBD disease activity was associated with anaemia. References: 1. Guideline on Haemoglobin Cutoffs to Define Anaemia in Individuals and Populations. World Health Organization; 2024. 2. Wine E, Aloi M, Van Biervliet S, et al. Management of paediatric ulcerative colitis, part 1: Ambulatory care—An updated evidence-based consensus guideline from the European Society of Paediatric Gastroenterology, Hepatology and Nutrition and the European Crohn’s and Colitis Organisation. J Pediatr Gastroenterol Nutr. 2025;81(3):765-815. doi:10.1002/jpn3.70097 Conflict of interest: Ms. Norup, Julie Rahbek: No conflict of interest Jansson, Sabine: Travel grant from Ferring Pharmaceuticals. Research grants from Ferring Pharmaceuticals and Takeda Pharma A/S. All unrelated to the submitted work. Malham, Mikkel: No conflict of interest Wewer, Vibeke: No conflict of interest
Norup et al. (Thu,) studied this question.