All populations are expressed as a percentage of CD45+CD19+CD20+ B-cells, unless otherwise specified. CD10+ B cells reflect immature B cells prior to the stage of transitional B-cells. While transitional B cells are characterized by a lack of CD27 and CD21, and high levels of CD38 and IgM. Mature, naïve B cells are CD27 negative, CD21 positive, and IgM and IgD positive. Peripheral blood memory B-cells are CD27 positive and can be further classified as non-switched memory (IgM positive and IgD positive or negative) or switched memory (IgM and IgD negative). Positive expression of CD5 on B cells may indicate a specific B-cell lineage or an in vivo activated B cell subset. Activated circulating B cells can be identified with the bright CD38 and down-regulated CD19 expression, wherein CD20 is already lost at this stage.

This flow cytometric assay is intended to provide a global overview of B-cell development and differentiation. This is performed using peripheral whole blood and specific combinations of surface markers. This test is clinically utilized to detect defects in the normal sequence of maturation and differentiation of B-cells through the absence of certain subpopulations, and/or the presence of unusual populations, not normally found in peripheral blood. In addition, aberrant B-cell function may be detected by alterations in the normal distribution of B-cell populations. Test results are intended for use in conjunction with other clinical and diagnostic information and should not be the sole determinant for patient diagnosis or management decisions.