Monoclonal B lymphocytosis

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Monoclonal B-lymphocytosis (MBL) as a distinct entity recognised in the WHO Classification and used to denote the presence of abnormal conal B-cells that do not meet the diagnostic criteria for CLL or other LPD based. It is an important distinction since affected individaual are not regarded as having a lymphoproliferative disorder, although they may experience some symptoms, and the disease may progress.

The diagnosis is suggested from flow cytometry of blood, but always requires clinical confirmation - it is important that reports reflect the need for additional clinical conformation.

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Diagnosis is made from blood assessment by flow cytometry and is based on the following criteria:

1. Flow cytometry defined features:

• Evidence that there is a monoclonal population of B lymphocytes (this can be based on their light chain retriction or abnormal phenotype features)

• A profile of by flow cytometry that suggests either CLL or other LPD, based on the abnormal gated population that may be a minority of cells

• A count of abnormal cells that is <1x10⁹ for the abnormal poulation (usually calculated from the gated abnormal poulation and the absolute lymphocyte count

2. Additional clinical evidence that there is no significant tissue disease:

• No evidence of lymph node enlargment or other significant tissue involvements by the abnormal cells

• No other features suggesting an active B-lymphoproliferative disease or lymphoma

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