**2. Diagnosis**

CLL diagnosis depends on the presentation. For patients presenting with absolute lymphocytosis; CBC, flow cytometry of the peripheral blood, and examination of the peripheral smear are adequate to diagnose CLL [2]. Diagnosis of CLL using these tests requires identification of absolute B lymphocyte count (B-ALC) >5000/micrL sustained for at least 3 months, morphologically mature-appearing

small lymphocytes, and flow cytometry showing the typical immunophenotype of CLL cells: extremely low levels of surface membrane immunoglobulin (SmIg) and either Kappa or Lambda (but not both), CD19, CD20, CD23 and CD5 positive cells. Evaluation of the bone marrow is not usually necessary, but is included in the evaluation of patients with unexplained cytopenias. Patients presenting with lymphadenopathy without lymphocytosis will need ideally an excisional lymph node biopsy or alternatively a needle biopsy showing mature lymphocytes with the previously mentioned phenotype to diagnose small lymphocytic lymphoma (SLL) which is considered by WHO the same disease as CLL with different manifestations [3].

Monoclonal B cell lymphocytosis is diagnosed when B-ALC is <5000/micrL persistently with no other manifestations of disease activity such as lymphadenopathy, hepatosplenomegaly, disease related cytopenias, or disease related symptoms. Patients with disease related cytopenias are diagnosed with CLL regardless of B-ALC and patients with any of the other manifestations are considered to have SLL [2]. Before 2008, the diagnosis of CLL was based on ALC equal or more than 5000/microL in the setting of appropriate immunophenotype. Patients with an absolute B lymphocyte count (B-ALC) less than 5000/microL and an ALC more than 5000/microL represented an overlap between CLL and monoclonal B cell lymphocytosis. The switch to using B-ALC for the diagnosis of CLL in 2008 eliminated this overlap [4, 5].
