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  • In adults, lymphocytosis is defined as an absolute lymphocyte count exceeding 4.0 × 109/L.

  • Normal lymphocyte count in childhood is higher than in adults (mean ~6.0 × 109/L) (see Chap. 6).

  • Table 50–1 lists the causes of primary and reactive lymphocytosis.

  • Examine blood film to determine if there is abnormal prevalence of:

    — Blasts, associated with acute lymphoblastic leukemia (see Chap. 55)

    — Small lymphocytes and smudge cells associated with chronic lymphocytic leukemia (CLL) (see Chap. 56)

    — Large granular lymphocytes associated with large granular lymphocyte leukemia (LGLL) (see Chap. 58)

    — Small cleaved lymphocytes associated with low- or intermediate-grade lymphomas (see Chap. 62)

    — Reactive lymphocytes associated with infectious mononucleosis (see Chap. 53)

  • Flow cytometric immunophenotyping of cell surface markers (CD), serum protein electrophoresis and immunofixation for monoclonal immunoglobulins, studies of T-cell–receptor gene rearrangement, or clonal cytogenetic findings can distinguish monoclonal lymphocytosis (B or T lymphocytic leukemia or lymphoma) from polyclonal (reactive) lymphocytosis.


Primary Lymphocytosis

Lymphocytic Malignancies

  • Referred to as lymphoproliferative disorders

  • Neoplastic accumulation of monoclonal B cells, T cells, natural killer (NK) cells, or less fully differentiated cells of the lymphoid lineage

Monoclonal B-Cell Lymphocytosis

  • Defined as the expansion of a monoclonal population of B cells with an absolute B-cell count of less than 5.0 × 109/L in the absence of organomegaly, lymphadenopathy, extramedullary involvement, and cytopenias.

  • Two groups (Table 50–2): ...

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