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

Predominance of Mononuclear Round to Oval Cells91Note that in about one-fourth of all leukemias total leukocyte counts arenormal, or even reduced, and the atypical round cells affect only the relative(differential) blood analysis (“aleukemic leukemia”).In all forms of leukemia, the more fluffy layered areas of a smear show thatthe nuclear chromatin structure is not dense and coarse, as in a normallymphocyte nucleus (p. 49), but more delicately structured and irregular,often “sand-like”. A careful blood cell analysis should be carried out—perhapswith the assistance of a specialist laboratory—before bone marrowanalysis is performed.In most cases, the high leukocyte count facilitates the diagnosis ofleukemia. Apart from the leukemia-specific blast cells, a variable numberof segmented neutrophilic granulocytes may also remain, depending onthe disease progression at the time of diagnosis. This gap in the cell seriesbetween blasts and mature cells is called “leukemic hiatus.” It is found inALL but not in reactive responses or chronic myeloid leukemia, whichshow a continuous left shift. Morphological or differential diagnosis ofacute leukemia is followed by the diagnostic work-up that continues withcytochemical tests. Immunological identification of leukemia cells is alwaysindicated (Table 14).Diagnostic work-up when acute leukemia is suspected:CBC, cytochemistry, bone marrow. Collection of material to identify cellsurface markers, cytogenetics, molecular genetics.Morphological and Cytochemical Cell IdentificationAfter a first-line diagnosis of acute leukemia has been arrived at on thebasis of the cell morphology (see above), the diagnosis must be refined bycytochemical testing of blood cells or bone marrow (on fresh smears).Table 14 shows a leukemia classification based on both morphological andcytochemical criteria. The table shows that a peroxidase test allowsleukemias to be classified as peroxidase-positive (myeloid or monocytic)or peroxidase-negative (lymphoblastic). The next step is the immunologicalclassification based on cell markers.In routine clinical hematology, the FAB classification (Table 14) will bewith us for a few more years.