As mentioned previously, one of the important first steps in diagnosis is whether the neoplastic disorder appears to be acute or chronic. To make this determination, count the percentage of blasts in the peripheral blood smear and also in the bone marrow smear. A general guideline is that if 20% or more blasts are found in one or both of these specimens, then it is an acute leukemia. This is an especially important distinction between AML and the chronic myeloid disorders (e.g. myelodysplastic syndromes (MDS) and myeloproliferative disorders (MPD), which may also be referred to as myeloproliferative neoplasms (MPN)).
The top image to the right shows numerous blasts in a blood smear of AML. Note the characteristic large nuclei with loose, lacey chromatin, high nuclear/cytoplasmic ratio, and the presence of nucleoli. Also, there are few representatives of other stages of maturation. Contrast this to the smear below which is from a patient with chronic myeloid leukemia (CML). Note that there are fewer blasts, and more mature cells. A number of maturation stages can be seen, such as myelocytes, metamyelocytes. and segmented neutrophils.
