From the Guidelines
Chronic Lymphocytic Leukemia (CLL) is classically diagnosed on a Complete Blood Count (CBC) with lymphocytosis, typically showing an absolute lymphocyte count greater than 5,000 cells/μL, which is the primary diagnostic finding, as stated in the most recent guidelines 1. The diagnosis of CLL requires the presence of at least 5 × 10^9 B lymphocytes/L (5000/L) in the peripheral blood, with the clonality of the circulating B lymphocytes confirmed by flow cytometry 1.
Key Diagnostic Features
- Lymphocytosis with an absolute lymphocyte count greater than 5,000 cells/μL
- Small, mature-appearing lymphocytes with condensed nuclear chromatin, inconspicuous nucleoli, and scant cytoplasm
- Characteristic "smudge cells" or "basket cells" (fragile lymphocytes that rupture during smear preparation)
- Flow cytometry confirming a monoclonal B-cell population with the characteristic CLL immunophenotype (CD5+, CD19+, CD23+, dim surface immunoglobulin expression) 1
Additional Diagnostic Considerations
- The presence of prolymphocytes in excess of 55% would favor a diagnosis of prolymphocytic leukemia (B-cell PLL) 1
- CLL cells co-express the CD5 antigen and B-cell surface antigens CD19, CD20, and CD23, with low levels of surface immunoglobulin, CD20, and CD79b compared to normal B cells 1
- Each clone of leukemia cells is restricted to expression of either λ or κ immunoglobulin light chains 1
From the Research
Chronic Lymphocytic Leukemia (CLL) Classic Findings on CBC
- CLL is characterized by an increased number of B-lymphocytes in the blood, typically more than 5000 B-lymphocytes/µl 2
- The diagnosis of CLL is established by blood counts, blood smears, and immunophenotyping of circulating B-lymphocytes, which identify a clonal B-cell population carrying the CD5 antigen as well as typical B-cell markers 3
- Classic findings on CBC in CLL patients include:
- Lymphocytosis (elevated lymphocyte count)
- Anemia (low hemoglobin level)
- Thrombocytopenia (low platelet count)
- The European Binet staging system is used to classify CLL into three stages (A, B, and C) based on the degree of lymphadenopathy, organomegaly, and cytopenias 2
- Patients with Binet stage A have 0 to 2 areas of node or organ enlargement with normal levels of hemoglobin and platelets, while those with Binet stage C have anemia and/or thrombocytopenia, with or without lymphadenopathy or organomegaly 2
Diagnostic Criteria
- The diagnosis of CLL requires the presence of more than 5000 B-lymphocytes/µl in the blood, as well as the expression of specific surface markers such as CD5, CD19, and CD23 2, 3
- Flow cytometry is used to confirm the diagnosis and to assess the expression of these surface markers 2, 3
- Imaging studies such as X-ray, ultrasound, or CT scan may be used to assess the degree of lymphadenopathy or organomegaly 2
Prognostic Factors
- The CLL international prognostic index integrates genetic, biological, and clinical variables to identify distinct risk groups of patients with CLL 3
- Deletions of the short arm of chromosome 17 (del[17p]) and/or mutations of the TP53 gene predict resistance to chemoimmunotherapy and a shorter time to progression with most targeted therapies 3