Patients developing inflammatory bowel disease have iron deficiency and lower plasma ferritin years before diagnosis: a nested case-control study.

BACKGROUND Iron deficiency is common among inflammatory bowel disease (IBD) patients, generally reported without comparisons with controls. The aim of this study was to analyse if iron deficiency was more common among those later developing IBD compared to matched controls in a prospective setting. METHODS We included 96 healthy subjects later developing IBD and 191 matched controls from the Northern Sweden Health and Disease Study. We analysed iron, ferritin, transferrin, and calculated transferrin saturation in plasma sampled at least 1 year prior to IBD diagnosis. Iron deficiency was defined as plasma ferritin 3 mg/L, iron deficiency could not be excluded if ferritin was <100 µg/L. RESULTS Iron deficiency could not be excluded among more male cases vs controls (25.0% vs 2.2%; P < 0.001), whereas with no differences for women (39.6% vs 35.3%; P = 0.538). Ferritin was lower among male IBD cases (P = 0.001) and for ulcerative colitis (P = 0.016 for males and 0.017 for females), but not for Crohn's disease. Ferritin was associated with a lower risk for IBD and in the ulcerative colitis subgroup when using sex-based z-scores. Ferritin quartiles 2-4 had a 65% lower odds ratio for all IBD, ulcerative colitis, and Crohn's disease in multivariable analysis. CONCLUSIONS Lower ferritin was associated with higher risk for developing IBD in a prospective setting. Iron deficiency was more common among healthy males years later developing IBD compared to matched controls, but not among women.