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Slide 1
This program, Microscopic Examination of the Bone Marrow, should follow the units Immature Cells in the Monocytic, and Lymphocytic Series and Nucleated Red Blood Cells. This program describes the other cells in the bone marrow (with special reference to the maturation of the megakaryocytes), how to do a bone marrow differential count on an aspirate stained with Wright's stain, and how to interpret the results.

There are three main reasons to examine the bone marrow: for diagnosis and for confirmation or exclusion of certain diagnoses, for evaluation of treatment, and for microbiologic culture. Bone marrow is also obtained for bone marrow transplantation and for study of in vitro hematopoiesis.

Bone marrow differentials are especially important for the beginner to do. Their value lies in identifying, categorizing, and counting each cell. Cells that are not recognized should be identified by someone more experienced. Another reason for doing a differential is to determine an accurate myeloid-to-erythroid ratio (M:E). Strictly speaking, "myeloid" refers to all phases of bone marrow activity and is not restricted to granulopoiesis. Although bone marrow differentials are important, experienced observers usually only scan the slide to determine if the bone marrow is nondiagnostic or diagnostic. In some laboratories, technicians do the actual bone marrow differentials but the bone marrow should be scanned and the report signed by the hematologist or pathologist responsibie for communicating with the attending physician.

The diagnoses that can be made from a microscopic examination are many. These include megaloblastic, refractory, and aplastic anemias, and if an iron stain is available, sideroblastic and iron deficiency anemias. Other diagnoses that can be made are leukemia; multiple myeloma; Waldenstrom's macroglobulinemia; and fungal, parasitic, and, rarely, bacterial infections. Inborn errors of metabolism that can be diagnosed are Gaucher's disease, Niemann-Pick disease, Chediak-Higashi syndrome, and cystinosis. Cancer can be diagnosed if cancer cells are seen. Then there is a class of poorly defined diseases of the reticuloendothelial system, which includes histiocytic leukemia, histiocytosis X, sea-blue histiocytosis, and other rare diseases, such as congenital erythrophagocytosis, and cyclic and congenital amegakaryocytic thrombocytopenia.

The conditions that cannot be definitively diagnosed but for which a bone marrow should be examined include thrombocytopenia (to note the quality and quantity of the megakaryocytes), polycythemia vera and myelofibrosis (to exclude leukemia), lymphoma (to assess the amount of bone marrow involvement), and hereditary erythrocytic multinuclearity with positive acidified serum (HEMPAS).

Many repeat bone marrow examinations are performed for evaluating the response to chemotherapy. Microbiological cultures are important to obtain in the diagnostic evaluation of fever of unknown origin, particularly if fungal infection or tuberculosis is suspected.

Bone marrow transplants (with bone marrow from compatible donors) now are being done in cases of aplastic anemia and leukemia. Autologous bone marrow transplants also are being used as supportive therapy following treatment of solid tumors with radiation and chemotherapy.

In vitro bone marrow cultures are maintained in some research laboratories to determine the effect of chemotherapeutic agents on cellular activity and to study the growth pattern in leukemia. So far, such procedures have little clinical value.

Bone marrow usually is obtained for both an aspirate and a biopsy from the tibia in children under one year of age and from the posterior iliac crest in older persons; however, bone marrow for microscopic examination may be obtained from the spinous process, anterior iliac crest, or sternum.

The next four photomicrographs and an additional six appearing later in the program are accompanied by questions. The cells to be identified are indicated by arrows.

Course Section: 06. Microscopic Examination of the Bone Marrow
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