Move from recognition to integrated resolution

Blast-like cells are immature-appearing cells, often with a high nuclear-to-cytoplasmic ratio, immature chromatin, and visible nucleoli. Myeloblasts may have fine chromatin, moderate cytoplasm, azurophilic granules, or Auer rods. Lymphoblasts can have scant agranular cytoplasm and variable nucleoli. Abnormal promyelocytes may be heavily granulated with irregular, folded, or bilobed nuclei and multiple or bundled Auer rods; less-granular or microgranular forms also occur. Reactive lymphocytes and other immature cells can overlap these appearances on a limited field, so morphology has meaningful limits.

An Auer rod supports myeloid differentiation when truly identified, but its absence does not exclude acute myeloid leukemia. Use a systematic smear description and preserve uncertainty until integrated studies are available. A qualified second review or escalation follows the validated local procedure; it is not a substitute for urgent communication when an urgent finding is present.

Flow cytometry can identify an abnormal population and support lineage and maturation assessment, but no single flow-cytometry blast gate—an analytical region used to enumerate a candidate population—or screening marker is definitive. Initial workup integrates morphology, flow cytometry, conventional cytogenetics, fluorescence in situ hybridization, or FISH, and molecular testing. Name the observed morphology and the concern, then route the specimen for studies that can resolve lineage and genetics.