Auer rod /ou″ər/ [John Auer, American physiologist, 1875–1948] , an abnormal, needle-shaped or round, pink-staining inclusion in the cytoplasm of myeloblasts and promyelocytes in acute myelogenous, promyelocytic, or myelomonocytic leukemia. These inclusions contain enzymes such as acid phosphatase, peroxidase, and esterase and may represent abnormal derivatives of cytoplasmic granules. The finding of Auer rods in stained blood smears helps to differentiate acute myelogenous leukemia from acute lymphoblastic leukemia.
