In patients with chronic lymphocytic leukemia (chronic lymphoid leukemia, CLL), the complete blood count (CBC) with differential shows absolute lymphocytosis, with more than 5000 B-lymphocytes/µL. Lymphocytosis must persist for longer than 3 months. Clonality must be confirmed by flow cytometry. The presence of a cytopenia caused by clonal bone marrow involvement establishes the diagnosis of CLL regardless of the peripheral B-lymphocyte count. Patients with fewer than 5000 B-lymphocytes/µL with lymphadenopathy and without cytopenias more likely have small lymphocytic lymphoma (SLL), although this diagnosis should be confirmed by lymph node biopsy.