Chronic lymphocytic leukemia other diagnostic studies

Determining clonality
The diagnosis of CLL is based on the demonstration of an abnormal population of B lymphocytes in the blood, bone marrow, or tissues that display an unusual but characteristic pattern of molecules on the cell surface. This atypical molecular pattern includes the co-expression of cells surface markers cluster of differentiation 5 (CD5) and cluster of differentiation 23 (CD23). In addition, all the CLL cells within one individual are functionally inert and clonal, that is genetically identical. In practice, this is inferred by the detection of only one of the mutually exclusive antibody light chains, kappa or lambda, on the entire population of the abnormal B cells. Normal B lymphocytes consist of a stew of different antibody producing cells resulting in a mixture of both kappa and lambda expressing cells. The lack of the normal distribution of kappa and lambda producing B cells is one basis for demonstrating clonality, the key element for establishing a diagnosis of any B cell malignancy (B cell Non-Hodgkin lymphoma).

Clonality is confirmed by the combination of the microscopic examination of the peripheral blood and analysis of the lymphocytes by flow cytometry. The latter is easily accomplished on a small amount of blood. A flow cytometer is an instrument that can examine the marker molecule expression on individual cells in fluids. This is accomplished using antibodies with fluorescent tags recognized by the instrument. In CLL, the lymphocytes are genetically clonal, of the B cell lineage (express marker molecules CD19 and CD20), and characteristically express the marker molecules CD5 and CD23. Morphologically, the cells resemble normal lymphocytes under the microscope, although slightly larger, and are fragile when smeared onto a glass slide giving rise to many broken cells (smudge cells).