Classification of Acute Leukaemia based on Blast Morphology, Cytochemistry and Flow Cytometry

Introduction: Acute leukaemias are a heterogeneous group of malignancies due to the abnormal proliferation of immature cells. The classification of acute leukaemia has been transformed over a period. French American British’s (FAB) classification of acute leukaemia is based on morphology and cytochemistry. Later, the World Health Organisation (WHO) classification stressed immunophenotyping to be done in the classification of acute leukaemia. Immunophenotyping is a powerful tool for classification and also for treatment and prognosis.

Aim: To study the morphology of blasts in the peripheral smear and bone marrow cytochemistry and to compare with immunophenotyping in the classification of acute leukaemia.

Materials and Methods: A prospective and cross-sectional study was undertaken in the Department of Transfusion Medicine and Immunohematology, at St. Johns National Academy of Health Sciences a Tertiary Care Hospital in Bengaluru, India, over a period of one year from November 2018 to October 2019. The morphology of the blast was studied in peripheral blood and bone marrow aspirate stained by Leishman stain. Cytochemistry in peripheral smear and bone marrow with Sudan Black B and Periodic Acid-Schiff (PAS) stain was done in all acute leukaemia. The flow cytometry samples were processed within 24 hours of collection of the samples with a panel of markers including myeloid and lymphoid lineage and precursor markers. The results of morphology were confirmed with flow cytometry and final reports were released. Microsoft excel was used to enter data.

Results: A total of 112 cases of acute leukaemia were studied and classified based on morphology, cytochemistry and immunophenotyping of blasts. A total of 46 cases of Acute Myeloid Leukaemia (AML) and 63 cases of Acute Lymphoblastic Leukaemia (ALL). Two cases were found with Chronic Myeloid Leukaemia (CML) in blast crisis, one with myeloid and another with lymphoid blast crisis. One biphenotypic leukaemia was noted. Sudan Black was positive in 35 (76%) of AML and PAS was positive in 28 (44%) of ALL. The most common AML subtype was AML-M2 and the most common ALL subtype was B cell ALL. The most common symptom was fever and the sign was pallor.

Conclusion: The present study showed that morphological diagnosis is important, based on which the cytochemistry and flow cytometry is performed for diagnosis. In cases of the diagnostic dilemma of acute leukaemia with morphology and cytochemistry, immunophenotyping supports diagnosing and classifying acute leukaemia.