In 1976, experts in blood cell morphology from France, the United States, and the United Kingdom discussed and developed diagnostic criteria for the typing of acute leukemia, so the initials of the three countries were used, referred to as the “FAB” typing.
According to the FAB criteria, which were revised in 1985, acute myeloblastic leukemia (AML) is classified into 8 subtypes from M0 to M7, and acute lymphoblastic leukemia (ALL) into 3 subtypes from L1 to L3.
AML is divided into the following 8 subtypes:
- M0: Undifferentiated AML
- M1: Acute myeloid leukemia minimally differentiated
- M2: Acute myeloid leukemia partially differentiated
- M3: acute promyelocytic leukemia
- M4: acute granulocytic-monocytic leukemia
- M5: acute monocytic leukemia
- M6: acute red leukemia
- M7: Acute megakaryocytic leukemia
ALL is divided into the following 3 subtypes:
- Type L1: Primary lymphocytes are predominantly small (≤12 μm in diameter), with little cytoplasm, regular karyotype, and small, indistinct nucleoli.
- L2 type: The primary young lymphocytes are mainly large cells (>12μm in diameter) with more cytoplasm, irregular karyotype, common depression or folding, and obvious nucleoli.
- L3: The primary lymphocytes are predominantly large cells, uniform in size, with a lot of cytoplasm, obvious vacuoles inside, basophilic cytoplasm, dark staining, regular karyotype, and clear nucleoli.
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This classification of acute leukemia is based only on cytomorphology, and therefore the diagnosis is not complete and has been gradually replaced by the MICM diagnostic criteria.