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Slide 17
Always do your differential with 1,000x magnification. Count at least 200-300 nucleated cells and report them as a percentage. Between 40-60 cells can be counted in one field with oil immersion. It becomes difficult with 100 or more cells, as we tend to skip or to count the same cells twice. Fewer than 10 cells per field indicates sinusoidal blood rather than actual bone marrow particles I divide the field into imaginary quarters and start at the 12-o'clock position and count clockwise. Beginners usually identify and categorize one cell at a time. I find it easier to count all the granulocytes in the field and then to go back over it and count the lymphocytes, nucleated red cells, plasma cells, and the other types in the same fashion. For instance, in this field there are 13 granulocytes. These are divided into two segs, four bands, four metamyelocytes, two myelocytes, and one promyelocyte (some promyelocytes do not contain granules). In addition to the granulocytes there are four normoblasts (E5) and two late erythroblasts (E4), one of which is in mitosis. There are also three naked nuclei, which are disregarded.

Course Section: 06. Microscopic Examination of the Bone Marrow
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