Color Atlas of Hematology - Practical Microscopic and Clinical ...

46Normal Cells of the Blood and Hematopoietic OrgansMonocytesMonocytes are produced in the bone marrow; their line of developmentbranches off at a very early stage from that of the granulocytic series (seeflow chart p. 3), but does not contain any distinct, specific precursors thatcan be securely identified with diagnostic significance in everyday morphologicalstudies. Owing to their great motility and adhesiveness, maturemonocytes are morphologically probably the most diversified of allcells. Measuring anywhere between 20 and 40 µm in size, their constantcharacteristic is an ovoid nucleus, usually irregular in outline, with invaginationsand often pseudopodia-like cytoplasmic processes. The fine,“busy” structure of their nuclear chromatin allows them to be distinguishedfrom myelocytes, whose chromatin has a patchy, streaky structure,and also from lymphocytes, which have dense, homogeneous nuclei.The basophilic cytoplasmic layer varies in width, stains a grayish color,and contains a scattered population of very fine reddish granules that areat the very limit of the eye’s resolution. These characteristics vary greatlywith the size of the monocyte, which in turn is dependent on the thicknessof the smear. Where the smear is thin, especially at the feathered end,monocytes are abundant, relatively large and loosely structured, and theircytoplasm stains light gray–blue (“dove gray”). In thick, dense parts of thesmear, some monocytes look more like lymphocytes: only a certain nuclearindentation and the “thundercloud” gray–blue staining of the cytoplasmmay still mark them out.Diagnostic Implications. In line with their function (see p. 5) as phagocyticdefense cells, an elevation of the monocyte population above 7% andabove 850/µl indicates an immune defense reaction; only when a sharprise in monocyte counts is accompanied by a drop in absolute counts inthe other cell series is monocytic leukemia suggested (p. 101). Phagocytosisof erythrocytes and white blood cells (hemophagocytosis) may occurin some virus infections and autoimmune diseases.➤ Monocytosis in cases of infection: always present at the end of acute infections;chronic especially in– Endocarditis lenta, listeriosis, brucellosis, tuberculosis➤ Monocytosis in cases of a non-infectious response, e.g.,– Collagenosis, Crohn disease, ulcerative colitis➤ Monocytoses in/as neoplasia, e.g.,– Paraneoplastic in cases of disseminating tumors, bronchial carcinoma,breast carcinoma, Hodgkin disease, myelodysplasias (especiallyCMML, pp. 107 f) and acute monocytic leukemia (p. 101)