Test Details: CD5 is a useful marker to categorize Chronic B-cell lymphoproliferative disorders (B-CLPD) in which there is a neoplastic accumulation of mature B- lymphoctes in the bone marrow, peripheral blood & lymphoid tissue. Most of these patients are positive for B cell markers on flow cytometry but a small population is negative. This negative group requires CD5 testing. CD5 negative B-CLPD cases usually have a leukemic phase of a well-defined lymphoma such as Marginal zone lymphoma, Lymphoplasmacytic lymphoma, Follicular cell lymphoma or Hairy cell leukaemia.