Table 2.

The WHO Classification of MDS

Disease	Peripheral blood criteria	BM Criteria
RA	Anemia, no or rare blasts	Erythroid dysplasia alone, <5% blasts, <15% ringed sideroblasts
RARS	Anemia, no blasts	Erythroid dysplasia alone, <5% blasts, >15% ringed sideroblasts
Refractory cytopenia with multilineage dysplasia	Cytopenias (bicytopenia or pancytopenia), no or rare blasts, no Auer rods, <1×109/L monocytes	Dysplasia in >10% of cells in >2 myeloid cell lines, <5% blasts, no Auer rods, <15% ringed sideroblasts
Refractory cytopenia with multilineage dysplasia and ringed sideroblasts	Cytopenias (bicytopenia or pancytopenia), no or rare blasts, no Auer rods, <1×109/L monocytes	Dysplasia in >10% of cells in >2 myeloid cell lines, <5% blasts, no Auer rods, >15% ringed sideroblasts
RAEB type 1	Cytopenias, <5% blasts, no Auer rods, <1×109/L monocytes	Unilineage or multilineage dysplasia, 5%–9% blasts, no Auer rods
RAEB type 2	Cytopenias, 5%–19% blasts, no Auer rods, <1×109/L monocytes	Unilineage or multilineage dysplasia, 10%–19% blasts, occasional Auer rods
MDS unclassified	Cytopenias, no or rare blasts, no Auer rods	Unilineage dysplasia in granulocytes or megakaryocytes, <5% blasts, no Auer rods
MDS associated with isolated deletion (5q)	Anemia, <5% blasts, platelet count normal to increased	Normal-to-increased megakaryocytes with hypolobated nuclei, <5% blasts, no Auer rods, isolated del (5q)

Abbreviations: BM, bone marrow; FAB, French, American, British classification of MDS; MDS, myelodysplastic syndromes; RA, refractory anemia; RAEB, refractory anemia with excess blasts; RAEB-t, refractory anemia with excess blasts in transformation; RARS, refractory anemia with ringed sideroblasts; WHO,World Health Organisation.