Horta-Baas G, et al. - A total of 699 candidates were assessed to examine red blood cell distribution width (RDW)and its clinical importance in subjects with osteoarthritis (OA), fibromyalgia (FM), rheumatoid arthritis (RA) and spondyloarthritis (SpA). They observed a significant increase in RDW within RA vs OA groups, active SpA vs OA, RA vs FM and active SpA vs FM groups. They preferred the presence of anisocytosis, a useful tool in discriminating the active articular inflammatory vs non-inflammatory diseases with 48–95% sensitivity and 66–95% specificity.