Blasts
Blasts are precursors of mature, circulating leukocytes. The classic blast is relatively large, has little to no visible cytoplasm and has a large round nucleus with a fine-grained chromatin pattern. In practice, blasts can take many different forms. Morphologically, no distinction can be made between lymphoid and myeloid blasts except for the presence of auer rods as these occur only in myeloid blasts.
Blasts are usually found in low numbers in the bone marrow and not in the peripheral blood. Only in extreme cases of stress-induced hematopoiesis (for example, due to a severe infection or recovery from a profound anemia), a single blast can be seen in peripheral blood. In almost all other cases, a chronic or acute malignancy is present.
The distinction below is based on flow cytometry, where blasts showed either myeloid (MPO) or lymphoid (CD19,CD10,CD22,cyCD79a) markers.
Myeloid
Lymphoid
