refractory anemia with ring sideroblasts refractory anemia with ring sideroblasts refractory anemia with ring sideroblasts is a type of myelodysplastic syndrome. rars is characterized by 5% or less myeloblasts in bone marrow. rars is distinguished from refractory anemia by having 15% or more ringed sideroblasts among the erythroid precursors in the bone marrow. refractory anemia with ring sideroblastsother namesrars