Inflammatory bowel disease (IBD) is a group of chronic gastrointestinal diseases with unknown cause and is characterized by frequent recurrence and recovery. A number of studies have recently referred to RDW as a marker of IBD. The present study was aimed at examining the diagnostic role of RDW as a new marker of inflammation to evaluate disease activity in patients with IBD.

A total of 100 patients with IBD including 29 patients with Crohn’s disease (CD) and 71 patients with ulcerative colitis (UC) as the experimental group and 50 healthy individuals who were homogeneous with regard to age and gender as the control group participated in the present study. The index of inflammatory disease activity among patients with CD and UC was determined through Crohn’s Disease Activity Index (CDAI) and Mayo Score, respectively. CD patients with CDAI≥150 and UC patients with Mayo Score≥3 were considered as active. Laboratory parameters such as RDW, ESR, PLAT, CRP, and WBC were measured for the patients with IBD, and compared in the active and inactive groups based on the type of the disease and presence of anemia.

RDW values were significantly higher in the patients with inflammatory bowel disease (CD, UC) compared to the control group (p=0.001). In the present study, based on the area under ROC curve, ESR is the best single marker of inflammation for the active form of IBD (P=0.01, AUC=0.842). Although the values related to RDW were not significant in order to distinguish the active and inactive forms of Crohn’s disease (P>0.05), these values were significant in the patients with the active form of ulcerative colitis (P<0.05), which indicates that the diagnostic accuracy of RDW as an inflammatory marker in distinguishing between the active form of ulcerative colitis is 72% and with a confidence of 95% between 63 to 86%.

According to the results of the present study, RDW can be valuable as a new marker of inflammation in monitoring patients in recovery phase and evaluate the activity of inflammatory bowel disease, especially to determine the disease activity in UC and CD patients with anemia.