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. The report should refer to the phenotype of the cells identifying either "CLL phenotype" or "non-CLL phenotype" based on the flow cytometry profile.

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Diagnosis is made from blood assessment by flow cytometry and is based on the following criteria that are both flow cytometric AND clinical:

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

AND

2. Clinical evidence that there is no detectable evidence of tissue disease or its effects:

• 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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