As noted, the sensitivity of the flow cytometry approach used for detection has a direct impact on the absolute numbers of CLL-phenotype cells that can be identified and hence the proportion of individuals with detectable CLL-like MBL. The initially proposed diagnostic criteria for MBL shown in Table 1 did not specify a flow cytometry analysis method, and were simply based on detection of a monoclonal B-cell population in the peripheral blood with an overall kappa:lambda ratio >3:1 or <0.3:1, or greater than 25% of B cells lacking or expressing low level surface immunoglobulin in conjunction with a disease-specific immunophenotype.(6) These criteria are primarily intended for diagnostic laboratories undertaking evaluation of samples referred for investigation of a suspected lymphoproliferative disorder. The ability to detect very small abnormal B-cell populations representing less than 100 cells/μL is generally not required and high-sensitivity approaches are not needed for routine diagnostic purposes.
