Auer rods are red staining, needle-like bodies that can be seen in the cytoplasm of myeloblasts and promyelocytes. Auer rods (see arrow in image) are cytoplasmic inclusions which result from an abnormal fusion of the primary (azurophilic) granules. Single or multiple Auer rods may be seen in the cytoplasm of a cell. If more than one is present, they are frequently close together and may even be overlapping.
Their identification is very important because, if found, they can confirm the presence of myeloblasts and/or promyelocytes indicating the possibility of an acute myeloid leukemia (AML). One particular form of AML called acute promyelocytic leukemia (APL) is known to have many promyelocytes with multiple Auer rods.
They can also be seen in a blast crisis in chronic myelogenous leukemia (CML). Auer rods are never seen in lymphoblasts. This differentiation is important because the treatment of lymphoblastic and myeloblastic leukemia are different.
Auer rods are always classified as pathological.
