“What am I looking at? ” Phagocytosis and particle internalization by cells in the urine is not common, but of clinical interest when it occurs. Phagocytosis/particle internalization can be observed in urine microscopy by the usual culprits: professional phagocytes like neutrophils and macrophages , but also by cells that we usually don’t think performs phagocytosis – that’s why the term “particle internalization” is used here.
Professional phagocytes like macrophages (Fig1) and neutrophils (Fig 2) are not a surprise but are still pretty neat to see in the urine sediment and can be confusing if you don’t expect them. In Fig 2, neutrophils are taking on a fungus particle much bigger than themselves!
What’s less expected, however, is non-professional phagocytes like renal tubular epithelial cells (Fig. 3) doing the same job.
Frequently, it is not an easy task to properly identify the phagocytic/particle internalization process, because the literature has infrequent examples, usually as case reports. Also, the identification of these “particles within other particle” usually requires proper microscopic resources like polarized light microscopy (Figures 3-5) and stains like Sternhemer-Malbin stain (Figure 2) or May-Grunwald-Giemsa stain (Figure 6).
However, independently of the availability of microscopic resources or stains, we need to be able to see that there is something unusual on the slide. As we are seeing here, virtually any particle (Figures 1-8) can be phagocytosed/internalized by both professional or non-professional phagocytes, from crystals, to microrganisms, from lipid droplets to cells [5,6].
There is a lack of published work on phagocytosis/particle internalization in the urinalysis subject, this is surely an opportunity for professionals interested on this field to develop works and clarify these very interesting findings.