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There are several kinds (subtypes) of MDS. Doctors classify MDS subtypes according to different factors. Doctors often use one of two systems to classify them: the French, American, British (FAB) classification system or World Health Organization (WHO) classification system.

Doctors also use the International Prognostic Scoring System (IPSS) to more narrowly define the degree of the disease's severity, determine patient risk factors and plan treatment.

FAB Classification

The table below shows the FAB classification system used by many doctors. The five FAB subtypes are based on bone marrow appearance and blood cell counts.



Refractory anemia (RA)
  • low levels of red cells (anemia)
  • mild to moderate decreases in levels of white cells and platelets
  • also called myelodysplasia
Refractory anemia with ringed sideroblasts (RARS)
  • RA, but with an abnormal accumulation of iron granules in developing cells called sideroblasts
  • also called acquired sideroblastic anemia or myelodysplasia
Refractory anemia with excess blasts (RAEB)
  • RA, but with clear signs of abnormal blast cells
  • sometimes called oligoblastic myelogenous leukemia to better describe the disorder
  • also referred to as smoldering leukemia but may not always progress slowly
Refractory anemia with excess blasts in transformation (RAEB-T)
  • RA, with a bone marrow blast count of 20 percent to 30 percent
Chronic myelomonocytic leukemia (CMML)
  • red cells, white cells and platelets may be affected
  • an increase in the number of monocytes (a type of white cell)
  • a small number of abnormal blast cells in the marrow

WHO Classification

A newer system sometimes used by doctors is the WHO classification system. It classifies MDS according to factors that differ from those of the FAB system:

  • considers molecular and chromosomal (cytogenetic) data
  • defines RAEB-T to be a leukemia rather than a subtype of MDS
  • defines patients with more than 20 percent blasts in marrow as having acute myeloid leukemia (AML)
  • includes the category of myelodysplastic syndromes/myeloproliferative diseases (MDS/MPD)
  • includes juvenile myelomonocytic leukemia (JMML) and chronic myelomonocytic leukemia (CMML) in the MDS/MPD category
  • includes the following subtypes:
    • 5q- syndrome
    • refractory cytopenia with multilineage dysplasia (RCMD)
    • unclassifiable MDS (MDS-u)
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last updated on Friday, March 16, 2012

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