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 a-naphthyl ace tate esterase (ANAE), and standardised methods for these cytochemistri es are detailed in this communication. For cases of acute leukaemia th at remain unclassified by primary cytochemistry, subsequent immunologi cal analyses for cytoplasmic CD3, CD22, MPO and nuclear TdT are recomm ended. The ICSH panel considers that the use of these minimum primary cytochemical and intracellular phenotyping procedures will lead to the consistent classification of most acute leukaemias, and that the thir d level of investigation (membrane immunophenotyping) should be used f or the purposes of confirmation, diagnostic clarification of atypical leukaemias, and the subtyping of acute lymphoblastic leukaemias (ALL). The ICSH panel also recognised that there are a number of additional 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 spe cialised laboratories, particularly in the areas of diagnostic researc h, will continue to use individual investigatory protocols, it is cons idered that the inclusion of the ICSH scheme as core components would lead to greater consistency when comparing independent studies of acut e leukaemia.