Side scatter versus CD45 flow cytometric plot can distinguish acute leukaemia subtypes

BACKGROUND & OBJECTIVES: Flow cytometry is an important tool to diagnose acute leukaemia. Attempts are being made to find the minimal number of antibodies for correctly diagnosing acute leukaemia subtypes. The present study was designed to evaluate the analysis of side scatter (SSC) versus CD45 flow dot plot to distinguish acute myeloid leukaemia (AML) from acute lymphoblastic leukaemia (ALL), with minimal immunological markers. METHODS: One hundred consecutive cases of acute leukaemia were evaluated for blast cluster on SSC versus CD45 plots. The parameters studied included visual shape, CD45 and side scatter expression, continuity with residual granulocytes/lymphocytes/monocytes and ratio of maximum width to maximum height (w/h). The final diagnosis of ALL and AML and their subtypes was made by morphology, cytochemistry and immunophenotyping. Two sample Wilcoxon rank-sum (Mann Whitney) test and Kruskal-Wallis equality-of-populations rank tests were applied to elucidate the significance of the above ratios of blast cluster for diagnosis of ALL, AML and their subtypes. Receiver operating characteristic (ROC) curves were generated and the optimal cut-offs of the w/h ratio to distinguish between ALL and AML determined. RESULTS: Of the 100 cases, 57 of ALL and 43 cases of AML were diagnosed. The median w/h ratio of blast population was 3.8 for ALL and 1 for AML (P<0.001). ROC had area under curve of 0.9772. The optimal cut-off of the w/h ratio for distinction of ALL from AML was found to be 1.6. INTERPRETATION & CONCLUSIONS: Our findings suggest that if w/h ratio on SSC versus CD45 plot is less than 1.6, AML may be considered, and if it is more than 1.6, ALL may be diagnosed. Using morphometric analysis of the blast cluster on SSC versus CD45, it was possible to distinguish between ALL and AML, and their subtypes.