The page below is a sample from the LabCE course Bone Marrow Aspiration: Normal Hematopoiesis and Basic Interpretive Procedures. Access the complete course and earn ASCLS P.A.C.E.-approved continuing education credits by subscribing online.

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Bone marrow Differentials

For the clinical laboratory professionals who are only familiar with peripheral blood morphology, the first few observations of bone marrow aspirate smears can be overwhelming. The difference in cellularity between the two sample types, not to mention the wider variety of cell types, can lead to mental and visual overload. It is important to step back and break it down into more manageable pieces, starting on low power.

Use low power (10x) to look at the distribution on the slide and the quality of the stain. Find areas where the spread/distribution of cells are thin enough (monolayer) to read easily and where you like the color balance and intensity of the stain. Next, add oil and move up to 50x and/or 100x power on the microscope.*

Remember that there are several different cell types that are normally present and develop in the bone marrow before heading out into the peripheral blood. Most hematology technologists are familiar with the myeloid maturation sequence from peripheral differentials, even if immature cells are less commonly seen. However, there are additional cell types that are not seen on the peripheral blood differential, since they reside only in the bone marrow. Becoming more familiar with these cell types and the maturation sequences of the myeloid, erythroid, and megakaryocytic cells found in normal bone marrows will make performing these differentials less intimidating.

One important concept to grasp is the continuum of cellular maturation sequences. There is no such thing as a magical switch that flips causing cells to jump to the next "textbook photo stage" as cell lines mature. Rather, each cell matures at its own pace. The maturation and morphology will vary from cell to cell and bone marrow to bone marrow. Understanding both nuclear and cytoplasmic normal morphology can aid in the identification of cells.

*As counter-intuitive as it sounds for most applications, higher magnification does not always help with morphology. Reserve 100x for ultra fine detail.