Diagnostic Performance of Red Cell Distribution Width in Adult Iraqi Patients with Ankylosing Spondylitis

BACKGROUND: Ankylosing spondylitis (AS) is a chronic, progressive inflammatory 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 modified New York classification 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: The mean age for patients and controls was 38.0 ± 9.0 and 35.8 ± 9.0 years, respectively (p=0.057). RDW was significantly higher in patients with AS compared with controls (14.133 ± 1.613 versus 12.299 ± 1.031, p < 0.001). There 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 differentiate between patients with AS and controls (AUC=0,84, p<0.001) and at optimum cut-off value>13% has highest accuracy (78.9%) with very good sensitivity test (81%) and NPV (85.6%) as well as good specificity (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 differentiate between patients with AS and controls.