french–american–british classification french–american–british classification the french–american–british (fab) classification systems refers to a series of classifications of hematologic diseases. it is based on the presence of dysmyelopoiesis and the quantification of myeloblasts and erythroblasts. it was first produced in 1976. types include: fab classification of acute lymphoblastic leukemias: l1–l3 (three subtypes) fab classification of acute myeloid leukemias: m0–m7 (eight subtypes) fab classification of myelodysplastic syndromes updates continued through at least 1989.