[Monoclonal B-cell lymphocytosis: physiological entity or preliminary stage of chronic lymphocytic leukaemia?].

The criteria for the diagnosis of chronic lymphocytic leukaemia (CLL) have recently been changed, with the absolute number of monoclonal B cells instead of the total number of lymphocytes now important. CLL is diagnosed when the number of monoclonal B cells with the characteristic CLL phenotype in peripheral blood exceeds 5 x 10(9)/l; fewer than 5 x 10(9)/l of monoclonal B cells with the characteristic CLL phenotype present in peripheral blood leads to a diagnosis of monoclonal B-cell lymphocytosis (MBL): a new diagnostic entity. The prevalence of MBL is estimated to be 3% and has a relatively mild course with a progression rate from MBL to CLL of 1-2% per year. After a single evaluation by a haematologist to exclude lymphadenopathy, organomegaly and infection as causes of the lymphocytosis, patients with MBL need only be evaluated once annually by their general practitioner for measurement of the blood lymphocyte count and referral in case of progression.