Objective. We investigated the association of platelet distribution width (PDW) and mean platelet volume (MPV) with disease activity indices of ankylosing spondylitis (AS) in patients whose laboratory results or medical conditions would not affect PDW and MPV levels. Methods. We analysed demographic and laboratory data of 88 patients with AS. On the same day as the laboratory tests were done, we assessed AS disease activity using the Bath Ankylosing Spondylitis Disease Activity Index, Bath Ankylosing Spondylitis Functional Index, Bath Ankylosing Spondylitis Patients Global Score and Ankylosing Spondylitis Disease Activity Score (ASDAS), including erythrocyte sedimentation rate (ESR) (ASDAS-ESR) and C-reactive protein (CRP) (ASDAS-CRP). The association was analyzed by linear regression. Results. The median age of 88 patients was 38.0 years and the median length of observation was 5.5 years. The median platelet count was 266,500.0/μL, the median PDW was 10.7 fL and the median MPV 9.6 fL. The median ESR was 19.0 mm/hr and CRP was 2.5 mg/L. Among acute reactants, only CRP was negatively correlated with MPV, but not PDW (r=−0.218, p＜0.041). However, both PDW and MPV were not significantly correlated with any disease activity index of AS. On multivariate linear regression analysis, only the length of observation was significantly correlated with MPV (β=0.224, p＜0.044). Conclusion. PDW and MPV were not potent surrogate markers to reflect AS activity, with potential confounding strictly controlled, to affect MPV and PDW levels.

Keywords: Mean platelet volume, Platelt count, Ankylosing spondylitis