Morphology and Cytochemistry

To make a diagnosis of AML at least 20 % blasts must be documented on a bone marrow aspirate smear. Common morphological features of AML include large blasts with abundant basophilic cytoplasm often containing azurophilic granules and perinuclear clearing. Auer rods are frequently found; they appear as long and sharp rods in the cytoplasm and are diagnostic of AML. Cytochemistry reveals that greater than 3 % of the blasts are myeloperoxidase or Sudan black positive; in case of M4 and M5 variants these can be negative but are classically nonspecific esterase positive. Morphological variations such as increase in monocytoid forms, abnormal erythroblasts or abnormal megakaryocytes are seen in different subsets of AML that can be diagnostic or may require additional cytochemistry or immunophenotypic information for accurate subtyping. Immunophenotypin