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Because there are so many different characteristics associated with myelodysplastic syndromes (MDS), a phenomenon that is sometimes referred to as prognostic heterogeneity, MDS is a difficult group of disorders to diagnose.

The diagnosis of myelodysplasatic syndromes typically begins with laboratory tests to measure red blood cell count, hematocrit, white blood cells and platelet counts. Chromosomal analyses and a bone marrow exam (bone marrow biopsy and aspiration) are typically performed.

Myelodysplastic syndromes is diagnosed when there is bone marrow failure and one or more of the following:

• There is an excess (> 5%) of immature cells or "blasts" in the bone marrow. Blast counts of 30% or higher in the bone marrow denote AML.

• There is a chromosome abnormality. Many patients with MDS have chromosomes or parts of chromosomes that are missing. These chromosome abnormalities are known as "deletions". These deletions may include -5 or -7, denoting that either the fifth or seventh chromosome is missing, respectively. In addition, some MDS patients may also have too many replications or "copies" of chromosome 8.

• Bone marrow cells show obvious "dysplasia" (abnormal appearance under a microscope).

• Other possible causes of bone marrow failure have been excluded. These include:

  • vitamin B12 deficiency
  • folic acid deficiency
  • iron deficiency