NCCN Guidelines for Patients® | Myelodysplastic Syndromes
19 NCCN Guidelines for Patients ® : Myelodysplastic Syndromes, 2018 2 Testing for MDS Genetic tests Bone marrow tests At the lab, a pathologist will view the bone marrow samples with a microscope. A pathologist is a doctor who’s an expert in testing cells and tissue for signs of disease. He or she will assess the size, shape, type, structure, and maturity of the cells in the sample. Doctors may refer to this as a morphologic assessment. During this assessment, the pathologist will note any signs of MDS, such as: Cells that have an abnormal size or shape (dysplasia). An abnormal number—too many or too few—of any types of blood cells. An increased number of young cells or very young cells (blast cells). More than the normal number of cells in the bone marrow—called hypercellular bone marrow. Less than the normal number of cells in the bone marrow—called hypocellular bone marrow. Red blood cells that have too much or too little iron. A key feature of MDS is that it causes dysplasia in one or more types of blood cells. In some types of MDS, red blood cells have too much iron. To check for this, a special dye called an iron stain is placed on the sample of liquid bone marrow. The excess iron shows up as small dots in a circle (ring) around the center of the cells. Thus, these cells are called ring sideroblasts. The number of blast cells in the bone marrow is important. In a healthy person, less than 5 percent of cells in the bone marrow are blast cells. This means that less than 5 out of every 100 bone marrow cells are blast cells. In a person with MDS, up to 19 percent of cells in the bone marrow may be blast cells. In some cases, MDS can progress to a more aggressive (fast-growing) cancer called AML. In AML, more than 20 percent of cells in the bone marrow are blast cells. The cell assessment and iron stain are not the only tests that will be done on the bone marrow samples. Your doctor wants to rule out other disease or syndromes in the bone marrow cells so the testing gets more specific. Tests of genes and chromosomes will also be done. These are called genetic tests and they are described in the next section. Genetic tests Cytogenetic testing Cytogenetic testing uses a microscope to examine the chromosomes inside of cells. This type of test is used to look for missing pieces or misplaced pieces (defects) in the chromosomes. It is often done on a sample of bone marrow. It can sometimes also be done on a sample of blood from your arm. For this test, cells are grown in a dish, and then frozen at the time that they are about to divide. A pathologist will then look at the chromosomes and line them up to make a “map” of the chromosomes under a microscope. This map is called a karyotype. The karyotype from your bone marrow will be compared with the karyotype from a normal man or woman to see if there are any changes in the size, shape, structure, or number of chromosomes in your bone marrow. About 50 percent of patients with MDS will have a normal karyotype, the rest will have one or more changes.