Table 1.

Overview of Studies that Reported the Frequency of MBL Among Healthy Residential Populations and Blood Donors

Authors, year (reference)	Country, study period, and study population	Laboratory tests and clinical evaluation	MBL criteria	Frequency of MBL N (%)
Dagklis et al., 2009 (12)	Italy 2005–2007 Healthy volunteers in a geographically isolated rural area  Total n: 1725  Age: 18–102 years  Male 758; female 967	Flow cytometry  Acquisition: 5 × 105 events/sample  Five color: CD20/CD5/CD19/k/λ PCR amplification of IGHV-D-J rearrangements and sequence analysis Clinical records	Mean B-cell count <5 × 109/L CLL-like:  CD5bright CD20dim expression on CD19+ B-cells with a normal or an unbalanceda k:λ ratio Non-CLL like:  CD5− MBL or atypical CLL-MBL with an unbalanced k:λ ratioa within CD5− or CD5+ B-cells	All MBL: 128/1725 (7.4%)  Male/female: (9.9%)/(5.5%) CLL-like: 89/1725 (5.2%)  Male/female: (6.7%)/(3.9%)  Age: <50 (0.8%), 50–69 (6.8%), >69 (9.2%)  Unbalanced k/λ ratio: 83/89  Monoclonal B-cells/total B-cells: (mean = 6.9%) Non-CLL-like: 39/1725 (2.3%) Age: <50 (1.3%), 50–69 (1.5%), >69 (5.1%) CD5− MBL: 20/1725 (1.2%)
Nieto et al., 2009 (13)	Spain 12 month period (not otherwise specified) Healthy volunteers from the primary health care system region of Salamanca  Total n: 608  Age: >40 years  Male 284; female 324	Flow cytometry   Acquisition: 5 × 106 leukocytes/sample  Eight color: CD20/CD45/CD8 +λ/CD56+k/CD4/CD19/CD3/CD38; CD20/CD45/Bcl2/CD23/CD19/CD10/CD5/CD38; CD20/k/λ/CD19/CD10/CD5 PCR amplification of IGH gene rearrangements	A clonal B-cell cluster of minimum 50 cellular events CLL-like: “Circulating monoclonal B-cells with a CLL-phenotype” Non-CLL like (not otherwise specified) Normal lymphocyte counts	All MBL: 87/608 (14.3%)  Age: 40–49 (5.1%), 50–59 (5.3%), 60–69 (17.5%), 70–79 (21.7%), 80–89 (27.3%), >89 (75.0%) CLL-like MBL: 73/608 (12.0%)  Male/female (13.8%)/(11.0%)  k Restricted: 48/73  λ Restricted: 11/73  Biclonal: 14/73  Monoclonal B-cells/total B-cells: (median = 0.38%) Non-CLL like: 14/608 (2.3%)
Shim et al., 2007 (20)	United States 1991–1994: baseline Volunteers living near or far from waste sites  Total n: 1,926  Age: 40–76 years  Male 934; female 992 1997, 2003: Follow-ups B-cell lymphocytosis cases at baseline only  Total n: 74	Flow cytometry:  Acquisition: not reported  Two color (baseline), three color (1997), four color (2003)  Extended panel for differential diagnosis (2003) Medical records review in the 2003 follow-up	MBL: CLL-like phenotype determined by “CD20, CD19, and CD5 staining patterns” or the presence of a monoclonal population determined by an unbalanceda k:λ ratio No known history of a lymphoproliferative disorder	Overall MBL: 11/1,926 (0.6%)  Baseline: 9 and 1997 follow-up: 2  Male/female (0.6%)/(0.5%)  Residents near waste sites (0.8%); far from waste sites (0.2%)
Rachel et al., 2007 (14)	United States 2000–2002 Blood donors in a blood center  Total n: 5141  Age: 17 years or older	Flow cytometry Acquisition: not reported Two-color screening (CD19/CD5) Extended panel for cases with ≥40% CD19+ or >15% CD19/5 coexpression: CD45, CD14, CD8, CD3, HLA-DR, CD2, CD19, CD10, CD20, CD23, CD7, k, λ PCR analysis for IGH gene clonality	B-cell count <5 × 109/L MBL: monoclonal B-cells expressing either “classical CLL” or “non-CLL subtypes” with a k:λ ratio >3:1 or <1:3	6/5141 (0.12%)  k Restricted: 1/5141 (0.02%)  λ Restricted: 5/5141 (0.1%)

^aunbalanced k:λ ratio: a k:λ ratio of >3:1 or <1:3