Monoclonal B-lymphocytosis: demographics, nature and subclassification in 414 community patients.

We analyzed patients with small B-cell clonal populations in a non-hospital based pathology laboratory servicing metropolitan and regional areas of New South Wales, Australia. There were 414 patients with a finding of a B-cell clone with total B-lymphocytes < 5.0 × 10(9)/L, fulfilling the criteria for monoclonal B-lymphocytosis (MBL). There were 212 males (51%) and 202 females (49%) with a mean age of 69.7 years. Patients could be clearly divided into two dominant groups: 322 (77.7%) with a typical chronic lymphocytic leukemia (CLL) phenotype, MBL[cll], and 92 (22.3%) with a "non-CLL" or lymphoma-like phenotype, MBL[nhl]. Analysis of MBL[cll] showed 168 (52.2%) males and 154 (47.8%) females with a mean age of 70.6 years. The mean clonal level (CD19/CD5+) was 2.36 × 10(9)/L and the absolute lymphocyte count (ALC) was 0.4-10.5 × 10(9)/L. The ALC was within the reference range (1.0-4.0 × 10(9)/L) in 22%. The 92 patients with MBL[nhl] were 44 (47.8%) males and 48 (52.2%) females, with a mean age of 66.7 years. The mean clonal level was 1.27 × 10(9)/L. There were 65 patients with a "lymphoma unclassifiable" clone and the remainder had a probable disease-specific diagnosis. In a large community cohort of patients, MBL can be divided into two dominant groups, MBL[cll] and the more heterogeneous MBL[nhl].