Estimated Glomerular Filtration Rate and the Risk of Inflammatory Bowel Disease in Adults: A Swedish Population-Based Study

Background Kidney complications are common in patients with long-standing inflammatory bowel disease (IBD). Whether kidney complications, defined as low estimated glomerular filtration rate (eGFR), may predispose to later IBD is unknown. Methods We analyzed the association between eGFR and the risk of being subsequently diagnosed with IBD among 1 612 160 adults from Stockholm. The exposure was categories of eGFR, with 90 to 104 mL/min/1.73 m(2) as the reference. Cox regression models were used to investigate the association between eGFR, IBD, and IBD subtypes. Subgroup analyses included age strata, sex, education, and comorbidities. To explore the possibility of detection bias or reverse causation, we estimated IBD hazard ratios (HRs) after excluding cases and individuals censored during early years of follow-up. Results During a median of 9 years of follow-up, we detected 9663 cases of IBD (3299 Crohn's disease, 5072 ulcerative colitis, 1292 IBD unclassified). Lower eGFR levels were associated with higher IBD risk (for eGFR 30-59 mL/min/1.73 m(2): adjusted HR, 1.15; 95% confidence interval [CI], 1.01-1.33; and for eGFR <30 mL/min/1.73 m(2): adjusted HR, 1.65; 95% CI, 1.16-2.37). This association was stronger in magnitude for Crohn's disease (for eGFR 30-59 mL/min/1.73 m(2): HR, 1.33, 95% CI, 1.04-1.72; and for eGFR <30 mL/min/1.73 m(2): HR, 2.25; 95% CI, 1.26-3.99). Results were consistent across strata of age, comorbidities, and attained education but suggested the association between eGFR and IBD to be stronger in women (P for interaction <.05). Results attenuated but were robust to exclusion of early IBD cases. Conclusions We observed an association between reduced eGFR and the risk of developing IBD, which was stronger in magnitude for Crohn's disease.