In a type of MDS called MDS-RS, immature red blood cells (RBCs)
pile up in the bone marrow. Many of these piled-up RBCs are a type of immature RBC called ring sideroblasts (RS). RS cells have a ring of small circular iron clumps around the center structure of the cell where most cells store DNA
. RS contribute to having low (red) blood cell counts.
How many RS you have is part of diagnosing your type of MDS. You can be diagnosed with MDS-RS if at least 15% (15 out of every 100) of your red blood cells are ring sideroblasts.