Occult B cell malignancies can be detected by three-color flow cytometry in patients with cytopenias

Patients with unexplained cytopenias often present a diagnostic dilemma wit h minimal morphologic or cytogenetic changes to identify the underlying dis ease process. We have used multidimensional flow cytometry in a study of pa tients with cytopenias and found that this technology established, changed, or refined the diagnosis in 17/121 patients. Using the flow cytometric tec hnique of CD45 and right angle light scatter (SSC) gating with two addition al markers in a three-color analysis, eight of 121 patients were found to h ave hairy cell leukemia (HCL), in the absence of definitive morphologic fin dings of HCL. Two additional patients were found to have non-Hodgkin's lymp homa (NHL). Myeloid abnormalities, myelodysplasia (MDS) or acute leukemia w as detected in seven of 56 patients with unexplained pancytopenia. Six of 6 5 patients identified with cytopenias resulting from lymphoid neoplasms had been referred for bone marrow transplantation (BMT) with a presumptive dia gnosis of MDS, with subsequent deferral of BMT upon correct diagnosis. The screening technique is incorporated into an extensive immunophenotyping sch eme to identify hematopoietic abnormalities using multidimensional flow cyt ometry (MDF). HCL cells (detected as low as 1.3%) reside in the same positi on as normal monocytes in the CD45 and SSC plots but could be distinguished from monocytes based on the expression of HLA-DR without CD11b, and expres sion of CD19. Further phenotyping of the abnormal population confirmed immu noglobulin light chain restriction, CD11c, and CD25 expression. Non-Hodgkin 's lymphoma was detected as aberrant mature lymphocytes expressing B lympho id markers, CD5 and right chain restriction. Myeloid abnormalities were ide ntified in the myeloblast or maturing myeloid cell fractions. The flow cyto metric scheme described can be used in primary diagnosis. The technique is definitive, sensitive, and stresses the importance of distinguishing lympho id from myeloid etiology of cytopenias.