Red Cell Distribution Width as an Independent Marker of Objective Disease Activity in Ulcerative Colitis and Crohn’s Disease: A Large Real-World Cohort of 1000 Patients

Abstract

Background/Aims: The treat-to-target (T2T) strategy requires objective biomarkers in inflammatory bowel disease (IBD). Red cell distribution width (RDW) is of interest and routinely available; however, its incremental diagnostic value beyond anemia and inflammatory markers for detecting endoscopic activity (and histologic activity in ulcerative colitis) remains unclear.

Materials and Methods: This retrospective cohort included 1000 IBD patients (ulcerative colitis (UC) = 580, Crohn’s disease (CD) = 420). Objective activity was defined endoscopically (UC: Mayo endoscopic subscore ≥2; CD: SES-CD ≥3), with histologic activity (Nancy Index ≥1) as a prespecified secondary endpoint in UC. Red cell distribution width was measured within a peri-endoscopic window (median 1 day; IQR 0-3). Diagnostic performance was assessed using receiver operating characteristic (ROC) analysis, reporting observed and optimism-corrected area under the curve (AUC). Incremental value over C-reactive protein (CRP) was evaluated using the DeLong method. Multivariable logistic regression was adjusted for anemia, iron-related parameters, inflammatory markers, disease extent, and medications.

Results: Active disease is present in 432 patients (43.2%). The RDW is higher in active vs. inactive disease (15.6 Å} 1.8% vs 13.9 Å} 1.4%; P < .001) and shows good discrimination (observed AUC 0.820; optimism-corrected AUC 0.815). A cut-off of 14.5% yield 78.9% sensitivity and 76.3% specificity. Adding RDW to CRP improve AUC from 0.845 to 0.880 (P = .002). Each 1% RDW increase independently predict active disease (adjusted OR 1.65; 95% CI, 1.30-2.09), including non-anemic patients. In UC, RDW increase with histological severity (P < .001).

Conclusion: Red cell distribution width independently reflects objective inflammatory activity in IBD and provides incremental value beyond standard markers, supporting its role as a low-cost adjunct for T2T monitoring.

Cite this article as: .zden Y. Red cell distribution width as an independent marker of objective disease activity in ulcerative colitis and Crohn’s disease: A large real-world cohort of 1000 patients. Turk J Gastroenterol. 2026;37(6):693-701.