ORIGINAL ARTICLE Increased Strength of Erythrocyte Aggregates in Blood of Patients with Inflammatory Bowel Disease Nitsan Maharshak, MD,* Yaron Arbel, MD, † Itzhak Shapira, MD, † Shlomo Berliner, MD, PhD, † Ronen Ben-Ami, MD, † Saul Yedgar, PhD, ‡ Gershon Barshtein, PhD, ‡ and Iris Dotan, MD* Background: Increased strength of red blood cell (RBC) aggre- gates are present during the acute inflammatory response and con- tribute to erythrocyte aggregation and may lead to microvascular dysfunction. Inflammatory bowel diseases (IBDs) are characterized by damage to the bowel wall. This damage may be at least partially attributed to microvascular ischemia caused by enhanced erythro- cyte aggregation. The aim of this study was to evaluate the strength of RBC aggregates in the blood of patients with IBD. Methods: The strengths of RBC aggregates were characterized by integrative RBC aggregation parameters, determined by measuring of RBC aggregation as a function of shear stress. The results are represented as the area under the curve (AUC) of aggregate size plotted against shear stress. For each patient, dynamic aggregation and disaggregation of RBC were recorded and analyzed according to the RBC aggregate size distribution at the different shear stresses. Aggregation indices were correlated with disease activity and in- flammatory biomarkers. Results: We examined 53 IBD patients and 63 controls. IBD patients had significantly elevated concentrations of inflammation- sensitive proteins and aggregation parameters. The strength of large aggregates, represented by AUC for large fraction aggregates, among patients (15.2  18.6) was double that of controls (7  10.9) (P = 0.006). The strength of large aggregates correlated with disease activity (r = 0.340; P  0.001) with concentration of fibrinogen (r = 0.575; P  0.001) and with concentration of high sensitivity C-reactive protein (r = 0.386; P  0.001). Conclusions: The strength of RBC aggregates is increased in patients with IBD and correlates with the intensity of the acute phase response. This could contribute to bowel damage in these diseases. (Inflamm Bowel Dis 2009;00:000 – 000) Key Words: erythrocyte aggregation, acute phase response T here are multiple lines of evidence to suggest a role for erythrocyte aggregation (EA) in the etiopathogenesis of microcirculatory slow flow, 1–9 tissue hypoxia, 10,11 endothelial dysfunction, 12 and reduced capillary density. 13 A detrimental microcirculatory rheological milieu might exist in patients suffering from inflammatory bowel disease (IBD) and a po- tential role of a compromised microcirculatory function has been suggested in the past in both patients and animal models of IBD. 14 –16 This may be responsible at least partially for tissue damage and necrosis present in the inflamed bowel wall. Several studies in the past have suggested the presence of increased EA in the peripheral blood of IBD patients. 17,18 We further explored this phenomenon by using a system that enables us to measure the strength of red blood cell (RBC) aggregates. In this research, we examined the role of cellular and plasmatic factors in aggregation of RBC from IBD pa- tients. A potential therapeutic intervention to reduce the ag- gregation might therefore be of interest. 19 –24 MATERILALS AND METHODS Study Design and Patient Selection We included IBD patients who were in routine follow- up at the IBD Center, Department of Gastroenterology and Liver Diseases, Tel Aviv Sourasky Medical Center (Tel Aviv, Israel). Excluded were individuals who had a recent (3 months) episode of infection and/or those with a history of malignancy. Disease activity of IBD was determined by using the Crohn’s Disease Activity Index (CDAI) scoring system for CD 25 and that of the Mayo Clinic for patients with ulcerative colitis (UC). 26 The control group included healthy volunteers, members of the medical staff, who had no under- lying process of infection/inflammation, did not take any steroidal or nonsteroidal antiinflammatory medication, and did not have any overt malignancy. Received for publication October 24, 2008; Accepted October 30, 2008. From the *Department of Gastroenterology and Liver Diseases, Tel Aviv Sourasky Medical Center, Tel Aviv, affiliated with the Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel, † Department of Medicine “D”, affiliated with the Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel, ‡ Department of Biochemistry, Hadassah School of Medi- cine, Hebrew University, Jerusalem, Israel. Drs. Dotan and Barshtein contributed equally to this article. Reprints: Iris Dotan, MD, IBD Center, Department of Gastroenterology and Liver Diseases, Tel Aviv Sourasky Medical Center, 6 Weizman St., Tel Aviv 64239 Israel (e-mail: irisd@tasmc.health.gov.il). Copyright © 2009 Crohn’s & Colitis Foundation of America, Inc. DOI 10.1002/ibd.20838 Published online in Wiley InterScience (www.interscience. wiley.com). Inflamm Bowel Dis 1