So from what I understand, the bone fragment with bone marrow attached is used by a genetics lab to pin point the exact type of leukemia you have. I think is a called a bone marrow aspiration. Where as a bone marrow biopsy is looking at the bone marrow in the blood. When I had both of them, the bone marrow was sent to a specialty lab (cancer lab) & their results were positive for monocytic leukemia. The bone with marrow attached was sent to a DNA/genetics lab and their results further defined it as chronic meylomonocytic Leukemia or CMML. There are three cells that make up white blood cells and the monocytes are the largest of the three. Hope this helps.