When blood test results indicate that a patient has anemia, with or without accompanying white blood cells and/or reduced platelets, the doctor may examine the patient’s bone marrow. Bone marrow tests may show abnormal bone marrow cells (such as abnormally developed cells) and chromosomal abnormalities (such as missing or increased chromosomes). These tests provide help to clarify the diagnosis. A bone marrow test consists of two parts: a bone marrow aspiration, in which bone marrow fluid is taken as a sample, and a bone marrow biopsy, in which a small piece of bone marrow tissue is spun as a sample. Usually the bone marrow aspiration and biopsy are performed at the same time. The physician or pathologist uses a microscope to examine the cells in the bone marrow puncture and biopsy samples. The doctor also tests the bone marrow for chromosomal abnormalities, which are made up of DNA and are contained in the nucleus of the cell. Because DNA contains information about proteins and other key biomolecules necessary for the synthesis of normal cell function, missing or damaged chromosomes can have serious consequences. The diagnosis of MDS can be clarified by chromosomal examination in nearly half of patients. Patients with MDS also require periodic bone marrow examinations to determine if their disease has progressed.