Clinical specimens of blood, bone marrow, lymph node, extranodal tissue, and body fluid were collected from 67 cases of hematologic neoplasms (including chronic lymphoid leukemias, T-and B-cell lymphomas, and acute lymphoblastic and myelogenous leukemias) for comparison between the right-angle light scatter (RALSVCD45 and the forward-angle light scatter (FALSVRALS gating combinations. One to three diagnostic markers were selected from each case, yielding 124 paired results for comparison. We found that the percentage of tumor cell isolation and the total cell count in the tumor cell gate were higher in RALS/CD45 than in FALS/RALS. When 20% was used as a cutoff point, 30 markers in FALS/RALS failed to identify the tumor population, Electronic isolation (gating) of t u m o r cells for immunophenotyping is one of the most important technical manipulations in flow cytometry for the diagnosis of leukemia and lymphoma. It is important because the instrument does not provide visual correlation between cellular morphology and markers. Traditionally, leukocytes are separated into three major groups (lymphocyte, granulocyte, and monocyte) by a combination of forward-angle light scatter (FALS) and right-angle light scatter (RALS). Although this gating strategy is ideal for separation of normal leukocytes in peripheral blood samples, it is not desirable for bone marrow or tissue specimens. In specimens other than peripheral blood, there is an excess of nonleukocytes exhibiting leukocytelike scatter characteristics leading to a low fraction of recovered leukocytes. while only 3 markers in RALS/CD45 failed to do so. The discriminative factor in the RALS/CD45 gating was mainly the CD45 intensity, whereas all cases except 3 showed low RALS. Although T-cell neoplasms showed a higher proportion of high CD45 intensity, other groups shared similar ranges of CD45 intensity, which is therefore of limited value for differential diagnosis. The RALS/CD45 combination produces higher recovery and purity for tumor cell isolation than the FALS/RALS combination and should replace the latter for routine immunophenotyping of lymphoma and leukemia.

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