Most bone marrow slides are made simply by placing a drop of bone marrow on a slide and using a smear preparation technique. However, in order to obtain consistently high-quality smears, it is necessary to select or concentrate the fragments on these smears.
Selecting or concentrating fragments can be performed with different methodologies. At the patient bedside, some clinicians will use the touch-preparation or pull-preparation method while tilting the slide to allow excess blood to roll off. This leaves more of the bone marrow spicules on the slide. This can be wasteful and rather messy but does not require a high level of skill.
A less wasteful method is to pour a portion of the marrow aspirate into a small petri dish and swirl it about, then tilt the dish to reveal the marrow spicules. These can then be extracted using a capillary pipette with a micro-pipette bulb and transferred to the slide for use in making smears. This technique allows the laboratory professional to make numerous smears containing fragments rather than relying on the random luck of the drop. Any excess marrow can be saved and returned to the EDTA tube for further testing. This capillary pipette concentration technique can be coupled with any of the smear preparation techniques but does require practice to perfect and maintain proficiency. When coupled with the coverslip method, it is possible to make two to three dozen quality smears from as little as 0.25–0.50 mL of marrow aspirate, making it ideal in small sample volume situations.
