Early reduction of serum immunoglobulin levels in patients with CLL. Serum IgM, IgG, and IgA levels in cMBL (clinical monoclonal B-cell lymphocytosis) and Rai stage 0, I-II, III-IV CLL at diagnosis are represented as dot plots. The normal aged-matched donor cohort was used as internal reference values and for statistical comparison. The bone marrow infiltration by CLL cells at the early and late stage of disease according to Rai classification is also represented.