Abstract Background The association between inflammatory bowel disease (IBD) and venous thromboembolism (VTE) is well-studied in the adult population. However, in paediatric-onset IBD (PIBD; 18 years) data are scarce. Most studies are limited in size, as pointed out by the recently published ESPGHAN-ECCO guidelines for the treatment of paediatric acute severe ulcerative colitis. Several studies have indicated an increased risk of cerebral venous sinus thrombosis (CSVT). Assessing the risk among children and adolescents across clinical characteristics is crucial to guide clinical decisions about prophylactic treatment. Methods We used data from nationwide population-based registers to identify patients diagnosed with PIBD in Denmark (1996-2022) and Sweden (2006-2023). Patients with PIBD were matched on the date of first IBD diagnostic listing with up to 10 reference individuals from the general population by age, sex, and place of residence. Occurrence of VTE was compared in absolute (incidence rate difference, IRD) and relative terms (hazard ratios, HR) with 95% confidence intervals (95%CI). Data from Denmark and Sweden were combined using random effects meta-analyses. Comparisons included VTE overall, by VTE subtypes, sex, age, IBD subtypes, and time since diagnosis; and in the data from Sweden only, by disease activity (steroid prescriptions or addition/change of immunomodulators or advanced therapies, hospitalisation or surgery for IBD) and hospitalisation. Results We included 4,009 (Denmark) + 6,781 (Sweden) patients with PIBD and 39,096 + 64,497 reference individuals. Median follow-up time was 9.6 and 8.9 years, respectively. The incidence rate of VTE among patients with IBD was 1.3 per 1,000 person-years (95%CI: 1.1-1.5), and 0.4 (95%CI: 0.2-0.7) among reference individuals, with an IRD of 0.9 (95%CI: 0.7-1.2) per 1,000 person-years and an HR of 3.3 (95%CI: 1.8-6.3) (Table 1). The HR within the first 2 years of IBD was 18.8 (95%CI: 10.3-34.1). While CSVT and other thrombotic events had the highest HRs among VTE subtypes, the absolute risk of CSVT was low, at 1 per 10,000 person-years. In Sweden, disease activity, and hospitalisation, particularly hospitalisation for IBD, were strongly associated with VTE. Conclusion PIBD was associated with a substantially increased relative risk of VTE compared to the general population, although the absolute risk, including that for CSVT, was very low. Clinicians should carefully consider the risk of VTE in this population, in particular early on in the disease course, and during disease activity and hospitalisation. Conflict of interest: Dr. Bröms, Gabriella: Dr Bröms has served as a speaker for Takeda and Janssen and worked on projects at Karolinska Institute, partly financed by Janssen, Pfizer and UCB, unrelated to this study. Trudu, Beatrice: None. Modin, Frederikke Agerbo: None. Moshtaghi-Svensson, John: None. Burisch, Johan: Dr. Burisch reports grants from AbbVie, Janssen-Cilag, MSD, Takeda, Tillots Pharma, Bristol Myers Squibb, and Novo Nordisk Foundation personal fees from AbbVie, Janssen-Cilag, Celgene, MSD, Pfizer, Takeda, Tillots Pharma, Bristol Myers Squibb, Samsung Bioepis, Pharmacosmos, Ferring, Galapagos, Eli Lilly, Dr Falk Pharma, Celltrion, Zealand Pharma and Orion Pharma. Forss, Anders: Served as speaker/advisory board member for Janssen Cilag AB, Pfizer and Tillotts Pharma. Jansson, Sabine: Dr Jansson has received travel support from Ferring Pharmaceuticals and research grants from Takeda Pharma A/S, and Ferring Pharmaceuticals. Unrelated to the work submitted. Ludvigsson, Jonas: Dr Ludvigsson has received financial support from Merck/MSD for a study on inflammatory bowel disease and fibrosis and for developing a paper reviewing national healthcare registers in China. Dr Ludvigsson also has an ongoing research collaboration on celiac disease with Takeda. Earlier support includes a grant from Janssen for an unrelated study on behalf of the Swedish IBD quality register (SWIBREG). Mårild, Karl: Dr Mårild has received payment for two lectures for Pfizer Osooli, Mehdi: Dr Osooli participated in projects at Karolinska institute partly financed by pharmaceutical companies. All unrelated to this study. de Ridder, Lissy: Non-financial Support: Pfizer Other: Abbvie, Pfizer, Janssen, Eli Lilly, Takeda, Medtronic, Alvotech Wewer, Vibeke: None. SWIBREG Study Group, Swibreg: None Malham, Mikkel: None. Olen, Ola: Dr Olén has led projects at Karolinska Institutet financed by grants from Pfizer, Janssen, Alfasigma, AbbVie, Takeda, Bristol Myers Squibb, and Ferring. OO has served as speaker for lectures organized by Janssen, Pfizer, Takeda, and Bristol Myers Squibb.
Bröms et al. (Thu,) studied this question.