20 to 60% of red cell precursors seen in bone marrow slides normally contain siderotic iron granules visible with Prussian blue stain. The presence of sideroblasts and siderocytes in the bone marrow indicates that the red cell precursors have an ample supply of iron. Neither sideroblasts nor siderocytes are present in normal peripheral blood.
When a red cell precursor contains too much iron, the siderotic granules form a ring around the nucleus. If five or more siderotic granules form a ring around at least half the periphery of the nucleus of a nucleated red blood cell, the cell is referred to as a ringed sideroblast. The ringed sideroblast is an abnormal (pathological) form of a sideroblast. The ringed sideroblast is associated with sideroblastic anemias and myelodysplasias. Ringed sideroblasts are indicated by the arrows in the image on the right.