The FAB system divides MDS into 5 subtypes. These subtypes include: Refractory anemia, also called RA. Refractory anemia with ring sideroblasts, also called RARS. Refractory anemia with excess blasts, also called RAEB. Refractory anemia with excess blasts in transformation, also called RAEB-t or AML. Chronic myelomonocytic leukemia, or CMML.