An Approach for Plasma Cell Myeloma Diagnosis by Two-Color Flow Cytometry Based on Kappa/Lambda Ratios of CD38-Gated Plasma Cells

Abstract

Criteria from the World Health Organization (WHO) are commonly used to diagnose plasma cell myeloma (PCM), but they are complex and require several laboratory parameters. To differentiate reactive plasmacytosis from clonal plasma cell neoplasms, such as PCM, it is important to accurately determine the expression ofthe cytoplasmic immunoglobulin (cIg) light chain (LC). Through retrospective analyses, we selected the patients with PCM, and analyzed records of 52 PCM patients, who underwent bone biopsies, and final diagnosis ofPCM was established according to WHO criteria, and 22 controls. In the present study, all samples were analyzed by flow cytometry (FC) in the side scatter vs CD38 histogram mode, and the CD38-gated plasma cell population was identified. The positive cell ratios of kappa and lambda to plasma cell populations were analyzed. PCM cells were distinguished from normal plasma cells by a cut-off level between 0.80 and 3.3, a sensitivity of 90.3%, and a specificity of 81.1%. Twocolor FC analysis is simple to perform, inexpensive, and clinically relevant data are obtained soon after completion of the FC measurements. It could be one of the helpful tools in the diagnosis of PCM. The correct diagnosis of PCM can be achieved more simply, efficiently, and rapidly by combining this method.Plasma cell myeloma (PCM) is a bone marrow (BM)-based, multifocal, plasma cell neoplasm associated with an M-protein in serum and/or urine. In most cases, tumor cells disseminated to the BM are involved. To diagnose PCM, criteria from the World Health Organization (WHO) are usually employed (1). They are based on a combination ofpathological, radiological, and clinical features. However, the diagnostic criteria are complex and several laboratory parameters are required for an appropriate diagnosis. The diagnosis involves evaluation of the clinical burden of plasma cell infiltration, analyses of radiologically detectable bone lesions, electrophoretic determination of monoclonal immunoglobulins (Ig), and assessment of plasma cells in the BM. Through retrospective analyses, we investigated the diagnostic value of an abnormal cytoplasmic kappa/lambda ratio of CD38-gated plasma cells assessed by flow cytometry (FC). We found the diagnostic range for the kappa/lambda ratio, which would allow to maximize the sensitivity and specificity of diagnosis, and to minimize false-positive and false-negative results.

Flow cytometry detection of CD138 expression continuum between monotypic B and plasma cells is associated with both high IgM peak levels and MYD88 mutation and contributes to diagnosis of Waldenström macroglobulinemia

“…Details of gating are given in the Supporting Information. Monotypic cases were those for which the kappa / lambda ratio was over 3 or below 0.5 for either B or PCs (Batata & Shen, 1993;Nakayama et al, 2013). Gating was then specifically done on monotypic cells.…”