Auer rods are elongated, azurophilic plasmic inclusions in leukaemic blasts belonging to the myeloid series. Their presence confirms the diagnosis of acute myeloid leukaemia. In promyelocytic leukaemia, there may be multiple such inclusion bodies, or they may even occur in clusters (faggots.) In acute leukaemia, spherically shaped, azurophilic structures (auer bodies) are also occasionally discovered in the cytoplasm of the myeloblasts. In promyelocytic leukaemia cells contain multiple auer rods or (faggots.) . Phi bodies are observed when dab is used . Phi bodies are observed in AML blasts and they are distinct from catalase – containing tissues. Like auer rods phi bodies appear to be characteristic of immature myeloid series but are seen more frequently than auer rods. Auer rods  are classically seen in myeloid leukaemias. They are named after John Auer an American Physiologist (1875-1948.) Blasts are classically seen in M1, M2, M3 and M4 acute leukaemias. In acute leukaemia, rods are composed of fused lysosomes and contain peroxidase, lysosomal enzymes, and large crystalline inclusions. They are also used to distinguish the pre-leukaemia myelodysplastic syndromes; refractory anaemia with excessts 2(which has Auer rods) from RAEB 1 (which does not).
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