1, peripheral blood B lymphocyte count ≥ 5 × 109 /L for at least 3 months 2, autologous cells in blood smear characteristically appear as small, mature lymphocytes with little cytoplasm, dense nuclei, inconspicuous nucleoli, and partially aggregated chromatin. Infantile lymphocytes in peripheral blood lymphocytes were <55%. 3. Typical immunophenotypic features: CD5(+), CDIO(-), CDl9(+), FMC7(-), CD23(+), CD43(+/-), CCND1(-). Surface immunoglobulin (sIg), CD20, CD22 and CD79b were weakly expressed (dim). Leukemia cells with restricted expression of light chains (i.e., only κ or λ light chains are expressed on the cell surface) 4. Exclude other chronic lymphoproliferative disorders that are easily misdiagnosed as CLL, such as condylomatous lymphoma, splenic marginal zone lymphoma, follicular lymphoma, lymphoplasmacytic lymphoma, hairy cell leukemia, and other small B-cell tumors with leukemia-like presentation. CLL should also be diagnosed if there is a typical bone marrow infiltration of slow lymphocytes causing hematocrit with a B lymphocyte count < 5 × 109 /L.