Abstract
Monoclonal B-cell lymphocytosis (MBL) is a recently described medical condition that displays biological similarities to the most common subtype of adult leukemia in the Western world, i.e. chronic lymphocytic leukemia (CLL). Diagnostic criteria have been published with the aim of differentiating between these two entities. The overall prevalence of MBL is at least 100 times higher than that of CLL, which indirectly suggests that MBL is not necessarily a pre-leukemic condition, although in some circumstances, CLL cases can really be preceded by MBL. In view of this high prevalence rate, general clinicians and even non-hematological specialists have a high chance of being faced with individuals with MBL in their routine clinical practice. MBL is classified as "clinical MBL", "population-screening MBL" and "atypical MBL" and the clinical management of affected individuals depends greatly on this differentiation. The present review provides a guide to diagnosing and following up MBL patients.