Auer rods are red-staining, needle-like bodies in the cytoplasm of myeloblasts and promyelocytes. Auer rods (see arrow in image) are cytoplasmic inclusions that 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 overlap.
Their identification is essential because, if found, they can confirm the presence of myeloblasts and/or promyelocytes, indicating the possibility of acute myeloid leukemia (AML). One particular form of AML, 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 significant because the treatment of lymphoblastic and myeloblastic leukemia is different.
Auer rods are always classified as pathological.
