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Rules for Bone Marrow Differentials

Bone marrow differentials have significant differences from peripheral blood differentials that need to be considered as they are reviewed and counted.

One of the most important facts to consider is the large variability in cellularity and cell distribution depending on the type of preparation that is used. Choosing where to count and when to use which of the smear types available to you, takes time and experience and can be directed by a pathologist's preference.

Regardless of how many, or what types of smears you have available to choose from, you will always start with a simple visual inspection of your smears.

  • Begin by recording the patient identification information as well as date of sample, and any other mandatory patient identifying information necessary for your laboratory.
  • Record aspiration site information when provided. Many patients will have bilateral bone marrow aspirates performed as part of a diagnostic or staging workup.
    • Standard aspiration sites are: posterior iliac crest (PIC), anterior iliac Crest (ANT), sternum (S), spinous process (SP) and sometimes in very young children, bone marrow is obtained from the tibia (T).
    • Be aware, that while a bilateral bone marrow aspirate usually involves an aspirate of the same site from opposite sides of the body, e.g., L-PIC and R-PIC, in some situations, a bilateral staging aspirate will be from two different compartments on the same side, e.g. R-AIC, R-PIC.
  • Observe the appearance of the bone marrow smears. Do any have feather edges? Are there fragments or spicules present on any of the smears available? If so, they should be your first choice to view, since they are more representative of what the biopsy will show if one was obtained.
  • Once you select your smears, scan using 10X magnification on the microscope. Are some of the fragments/smears so thick that you cannot see good morphology? If so, reject these areas/slides. Are some of the fragments/smears so thin that everything is smashed? These areas/smears cannot be used either. Are there areas in the vicinity of any of the fragments that have good staining characteristics as well as readable morphology? This is where you should begin your differential.