RECOMMENDED PROCEDURES FOR THE CLASSIFICATION OF ACUTE LEUKEMIAS

The classification of acute leukaemias is now widely based on a combin ed morphological, cytochemical and immunophenotyping approach. Difficu lties are frequently encountered however in reaching an acceptable deg ree of diagnostic concordance between different laboratories because o f variations in the techniques used (in terms of methodologies, reagen ts and equipment) and diagnostic interpretation. The International Cou ncil for Standardization in Haematology (ICSH) convened an expert pane l to consider currently available diagnostic techniques with the aim o f defining a minimum cytochemical and immunological diagnostic panel t hat could be used as core components for the classification of acute l eukaemia. The proposed ICSH scheme, which attempts to balance the basi c requirement for providing precise and informative diagnostic informa tion without limiting its use to only those laboratories with sophisti cated facilities, is based on three sequential levels of investigation ; primary cytochemistry, intracellular phenotyping and membrane immuno phenotyping. The minimum ICSH recommended cytochemistries comprise mye loperoxidase (MPO), chloroacetate esterase (ChlorE) and alpha-naphthyl acetate esterase (ANAE), and standardised methods for these cytochemi stries are detailed in this communication. For cases of acute leukaemi a that remain unclassified by primary cytochemistry, subsequent immuno logical analyses for cytoplasmic CD3, CD22, MPO and nuclear TdT are re commended. The ICSH panel considers that the use of these minimum prim ary cytochemical and intracellular phenotyping procedures will lead to the consistent classification of most acute leukaemias, and that the third level of investigation (membrane immunophenotyping) should be us ed for the purposes of confirmation, diagnostic clarification of atypi cal leukaemias, and the subtyping of acute lymphoblastic leukaemias (A LL). The ICSH panel also recognised that there are a number of additio nal technologies which can provide definitive diagnostic information, such as cytogenetics and DNA genotyping, but these were excluded from the minimum panel because of their restricted availability. While many specialised laboratories, particularly in the areas of diagnostic res earch, will continue to use individual investigatory protocols, it is considered that the inclusion of the ICSH scheme as core components wo uld lead to greater consistency when comparing independent studies of acute leukaemia.