Peripheral smear from a patient with the microgranular (or hypogranular) variant of acute promyelocytic leukemia (APL)

The white blood cell count in the microgranular (or hypogranular) type of APL is usually elevated, and the cells are identified by their bi-lobed, dumbbell-shaped, or reniform nuclei. The cells have no recognizable granules, but granules are in fact present and can be seen by electron microscopy. Despite the sub-light microscopic nature of the granules, the cells are still strongly positive for the myeloperoxidase reaction.