Types | Aplastic Anemia and MDS International Foundation


MDS classification systems divide MDS into subtypes based on the results of blood and bone marrow tests. Scoring systems such as IPSS and IPSS-R have been developed to determine the severity of the MDS, probable survival term, and the risk of MDS developing into acute myeloid leukemia (AML).


French American British (FAB) Classification System

The FAB system divides MDS in to five subtypes based on percentage of blasts in the bone marrow and the peripheral blood. It is now used less frequently than the WHO classification, but is included here as a reference.


% blasts in blood

% blasts in bone marrow

RA (Refractory Anemia)

< 1

< 5

RARS (Refractory Anemia with Ring Sideroblasts

< 1

< 5

RAEB (Refractory Anemia with Excess Blasts in Transmission) Note: Now called AML (acute myelogenous leukemia)

< 5

5 - 20

RAEB-t (Refractory Anemia with Excess Blasts in Transformation)

> 5

21 - 30

CMML (chronic myelomonocytic Leukemia)

> 5

5 - 20

WHO (World Health Organization) Classification System

The WHO classification system builds and expands on the older FAB system. It divides MDS into eight subtypes based on tests of the blood and bone marrow. These eight subtypes include:

MDS Subtype

Blood Findings

Bone Marrow Findings

RCUD (Refractory Cytopenia with Unilineage Dysplasia)


Considered the mildest category. MDS is limited to one cell line. There is little dysplasia.

Has 3 subtypes:

Less than 5 percent young blood cells (blasts) – applies to RA, RN and RT

  • Red cell dysplasia (cells with an abnormal size, shape, or look)

  • White cell dysplasia

  • Megakaryocyte dysplasia

RARS (Refractory anemia with ring sideroblasts, pronounced SID-uh-ruh-blasts)


In RARS, more than 15 percent red blood cells that contain ring-shaped iron deposits (ring sideroblasts)

RCMD (Refractory Cytopenia with Multilineage Dysplasia)

Low white blood cell count (neutropenia) or low platelet count (thrombocytopenia)

Dysplasia in more than 1 cell type

Less than 5% blasts, or less than 15% ringed sideroblasts

Note: In patients with more than 15% ringed sideroblasts, the subtype is called RCMD_RS

RAEB-1 (Refractory Anemia with Excess Blasts)

The same as refractory anemia

5% tp 9% blasts in marrow

Normal number of blasts in blood

RAEB-2 (Refractory Anemia with Excess Blasts 2)

Similar to  refractory anemia

10% to 19% blasts in marrow

May have blasts in blood

Isolated Del 5q (Deletion 5q)

The same as refractory anemia, plus normal or high platelet count

Deletion of chromosome 5q, with no other chromosome abnormality

Note: More common in women age 65 and older who have mild to moderate degrees of anemia, low white blood cell counts, and normal to high platelet counts; life expectancy of more than five years from time of diagnosis

RCC (Refractory cytopenia in childhood)

Often more than one low blood count.

Bone marrow is often empty of cells (hypocellular)

This is rare

Unclassified MDS

Low count for wither platelets or white blood cells

Unusual features, such as scarring (fibrosis) of the bone marrow

Note: Just 1% to 2% of MDS patients have this subtype

International Prognostic Scoring System (IPSS)

The IPSS gives each patient a score to help their doctor understand how quickly their MDS is progressing and what is likely to happen to their disease over time. Both IPSS and IPSS-R were developed from patient data obtained prior to treatment. Survival terms may be extended for patients who are undergoing treatment. The IPSS score assigns patients a score based on three factors:

Each factor gets a score.



IPSS Score

Blasts in bone marrow

less than 5%
5% to 10%
11% - 20%
21% - 30%


Cell DNA changes (cytogenics)



Low blood counts or cytopenias

0 or 1 cytopenia
2 or 3 cytopenias


Together, the scores tell which risk group you fall into.

  • If your IPSS score is 0, you are in the low-risk group.
  • If your IPSS score is 0.5 to 1, you are in the intermediate-1 risk group.

Low and Intermediate-1 risk categories are together considered lower-risk MDS.

  • If your IPSS score is 1.5 to 2, you are in the intermediate-2 risk group.
  • If your IPSS score is more than 2.5, you are in the high-risk group.

Intermediate-2 and High-Risk categories are together considered higher-risk MDS.

IPSS Prognostic Risk Categories, Scores, and Estimated Survival

Subtype Score
Low 0
Intermediate I 0.5 - 1.0
Intermediate II 1.5 - 2.0
High > 2.5

Revised International Prognostic Scoring System (IPSS-R)

The primary difference from IPSS is its treatment of the three primary variables for assessing MDS: blast percentages, cytopenias, and type and degree of chromosomal abnormalities (karyotype). Compared with the IPSS, the IPSS-R updates and gives greater weight to cytogenetic abnormalities and severity of cytopenias, while reassigning the weighting for blast percentages. Although IPSS is more widely used, it is anticipated that it will eventually be replaced by IPSS-R as more physicians and patients become familiar with it.

IPSS-R Cytogenetic Score

Prognostic subgroups Cytogenetic Abnormalities
Very Good -Y, del(11q)
Good Normal, del(5q), del(12p), del(20q), double incl. del(5q)
Intermediate del(7q), +8, +19, i(17q), any other single or double independent clones
Poor -7, inv(3)/t(3q), del3q, double including -7/del(7q), Complex: 3 abnormalities
Very Poor Complex: > 3 abnormalities

IPSS-R Prognostic Score Values

Prognostic Variable 0 0.5 1.0 1.5 2 3 4


Very Good   Good   Intermediate Poor Very Poor

Bone Marrow Blasts (%)

≤ 2 __ >2 - <5   5 - 10 > 10 __


≥ 10


8 - <10

< 8





≥ 100


< 50






≥ 0.8

< 0.8






IPSS-R Prognostic Risk Categories/Scores

Risk Category Risk Score
Very Low ≤ 1.5
Low > 1.5-3
Intermediate > 3-4.5
High > 4.5-6
Very High > 6

Both IPSS and IPSS-R were developed from patient data obtained prior to treatment. Survival may be extended for patients who are undergoing treatment. Ask your doctor about your score.

The Risk of Getting AML (Acute Myelogenous Leukemia)

AML is a cancer of the white blood cells. It is defined as having more than 20 out of every 100 white blood cells in the bone marrow which are immature white blood cells called blasts.

In people with AML, blasts make copies of themselves quickly. This slows the production of red blood cells, which causes a low red count (anemia). It also slows the production of platelets, which leads to a greater risk of serious bleeding.

Over time, some cases of MDS become AML. But most do not. Your risk of developing AML depends largely on which MDS subtype you have. The following subtypes are more likely to become AML:

  • If you have RA (Refractory Anemia) or RARS (Refractory Anemia with Ringed Sideroblasts), you have a 1 in 10 to 2 in 10 chance of developing AML.
  • If you have RAEB-1 (Refractory Anemia with Excess Blasts) or RAEB-2, you have a greater than 4 in 10 chance of developing

History of Classification

Before 1976, the term "MDS" didn't exist. Doctors and scientists used other names for what we now call MDS. At that time, there was no standard way to split MDS into subtypes.

In 1976, scientists came out with the first system for classifying MDS into subtypes. This system is called the French-American-British or FAB system. It is based on how blood and bone marrow cells look.

In 1997, the International Prognostic Scoring System or IPSS was launched. This system turns patient data into a score. The score tells how quickly an MDS case is likely to progress and helps predict what may happen with the patient's MDS in the future.
In 1999, the World Health Organization, or WHO, published a new classification system. This classification system was then revised in 2008. Its goal was to be more specific than the FAB in describing subtypes and in predicting what will happen to patients. The system is based on patient data from around the world and on the most up-to-date knowledge of MDS.

In 2011: Based on information gained from studies of many thousands more MDS patients since the introduction of IPSS, a revision to the standard IPSS, (IPSS-R) was introduced.

Your score helps your doctor answer the following questions:

  • How severe is your case of MDS?
  • How likely is your case to become AML (acute myelogenous leukemia)?
  • How long are you likely to live?