- Bone marrow aspirate or biopsy must contain ≥ 20% blasts of all nucleated cells or differential blood count must contain ≥ 20% blasts. In AML FAB M6 ≥ 30% of nonerythroid cells in the bone marrow must be leukemic blasts. In AML defined by cytogenetic aberrations, the proportion of blasts may be < 20%.