Research Article Diagnostic Performance of Red Cell Distribution Width in Adult Iraqi Patients with Ankylosing Spondylitis Faiq I. Gorial 1 and Ali M. Hassan 2 1 Rheumatology Unit, Department of Medicine, Collage of Medicine, University of Bagdad, Iraq 2 Baghdad Teaching Hospital, Rheumatology Unit, Baghdad, Iraq Correspondence should be addressed to Faiq I. Gorial; faiqig@gmail.com Received 10 January 2018; Revised 1 June 2018; Accepted 11 June 2018; Published 5 August 2018 Academic Editor: Marco Amedeo Cimmino Copyright © 2018 Faiq I. Gorial and Ali M. Hassan. Tis is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Background. Ankylosing spondylitis (AS) is a chronic, progressive infammatory rheumatic disease that leads to structural damage, functional impairment, and decrease in the quality of life. Red cell distribution width (RDW) is a part of the complete blood count (CBC) and estimates erythrocyte variability. Objective. To analyse RDW in patients with AS and to evaluate the relationships with acute phase reactants (APRs) and disease activity index. Patients and Methods. A total of 100 patients with AS (78 males and 22 females) were diagnosed according to the modifed New York classifcation criteria for AS and 146 (99 males: 47 females) healthy individuals matched in age and sex as controls enrolled in the study. Demographic data, disease activity scores using Bath Ankylosing Spondylitis Disease Activity Index (BASDAI), medical history, C-reactive protein (CRP), erythrocytes sedimentation rate (ESR), and complete blood count (CBC) were measured. Results. Te mean age for patients and controls was 38.0 ± 9.0 and 35.8 ± 9.0 years, respectively (p=0.057). RDW was signifcantly higher in patients with AS compared with controls (14.133 ± 1.613 versus 12.299 ± 1.031, p < 0.001). Tere was a direct correlation of RDW with both ESR and CRP (P < 0.001); RDW had r=0.38 for C-reactive protein (CRP) and r=0.413 for ESR. Also BASDAI was directly correlated with RDW (r=0.326 p<0.001). RDW was a valid measure to diferentiate between patients with AS and controls (AUC=0,84, p<0.001) and at optimum cut-of value>13% has highest accuracy (78.9%) with very good sensitivity test (81%) and NPV (85.6%) as well as good specifcity (77.4%) and PPV (71.1%). Conclusion. RDW was higher in AS patients compared with controls and was directly correlated with ESR, CRP, and BASDAI. RDW was a valid simple measure with good accuracy to diferentiate between patients with AS and controls. 1. Introduction Ankylosing spondylitis (AS) is a chronic, progressive infam- matory rheumatic disease that afects the axial skeleton causing characteristic back pain, structural and functional impairment, and decrease in the quality of life [1]. In Iraq, the estimated prevalence of AS is 0.13%, where 84% are HLA-B27 positive, while 2.1% of healthy populations are HLAB27 positive [2, 3]. Te collective impact of AS has a substantial infuence on patients’ quality of life. Over 75% of patients are able to remain in employment and enjoy a good quality of life [4]. Te RDW is a parameter of complete blood count (CBC) [5, 6]. RDW is a numerical measure that describes red blood cell volume heterogeneity and serves as a component of complete blood count in the diferential diagnosis of anaemia [7]. In fact, RDW has been shown to be strongly associated with CRP and ESR in a large cohort of unselected outpatients [8]. In addition, recent studies have shown that RDW was associated with the severity of rheumatoid arthritis (RA) [9], infammatory bowel diseases (IBDs) [10], and Behcet’s disease (BD) [11]. Two new studies had also determined that RDW was increased in patients with systemic lupus erythematosus (SLE) and related with SLE disease activity index (SLEDAI), ESR, and CRP [12]. Tis study aimed to evaluate serum RDW in patients with AS and to assess its relationships with APRs and AS disease activity index. Hindawi Arthritis Volume 2018, Article ID 2904694, 5 pages https://doi.org/10.1155/2018/2904694