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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One of the normal roles of the marrow macrophage is to remove cellular debris. In a normal bone marrow, this includes the engulfment of extruded RBC nuclei and old, non-nucleated RBCs at the end of their lifespan.

In some patients, macrophages lose their ability to distinguish self from non-self (i.e., invader/ pathogen) and good cells from old/senescent cells. This can happen because of an inborn error in the macrophages or by an infection-mediated transformation. When this change occurs, any cell in the vicinity of a defective macrophage become a target for engulfment. This term is called hemophagocytosis.

The top image on the right shows two macrophages that have ingested several different cell types (see red arrows). There is the normally ingested non-nucleated RBC, but also the abnormally ingested segmented neutrophil and at least one early nucleated RBC precursor. Viable bone marrow precursors are not the usual diet of macrophages.

The lower image on the right shows an even more impressive macrophage with at least a dozen or more ingested RBCs as well as three segmented neutrophils and a lymphocyte.