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

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.

To analyse RDW in patients with AS and to evaluate the relationships with acute phase reactants (APRs) and disease activity index.

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.

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%).

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.