Auer rods are red staining, needle-like bodies seen in the cytoplasm of myeloblasts, and/or progranulocytes in certain leukemias. 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 indicating the presence of a non-lymphocytic (myeloid) leukemia. They can also be seen in myeloid blast crisis in chronic granulocytic leukemia. 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.