Immunoglobulin M concentration in Waldenström macroglobulinemia: correlation with bone marrow B cells and plasma cells.

Serum immunoglobulin (Ig) M levels vary considerably among patients with Waldenström macroglobulinemia, and previous studies have failed to demonstrate a correlation with overall bone marrow disease burden. In this study, bone marrow B cells and plasma cells were enumerated by flow cytometry and correlated with serum IgM concentrations. Monotypic B cells comprised a median of 6% of bone marrow leukocytes but did not correlate with IgM levels (r = 0.071, P = .5). Plasma cells, although typically present in lower numbers (median, 0.52%) did show a correlation with IgM (r = 0.452, P = .01). IgM levels in Waldenström macroglobulinemia, at least in part, correlate with the degree of plasma cell differentiation seen within the tumor.