The page below is a sample from the LabCE course Body Fluid Differential Tutorial. Access the complete course and earn ASCLS P.A.C.E.-approved continuing education credits by subscribing online.

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The large multinucleate macrophage indicated by the arrow in this BAL is a histiocyte.

Notice the similar cytoplasmic characteristics and chromatin texture and staining between the histiocyte and macrophages. In fact, the terms "histiocyte" and "macrophage" are sometimes used interchangeably. The choice of which term to use can be institution- and pathologist-dependent. Some institutions designate large multinuclear macrophages as histiocytes.