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  • Adults: absolute lymphocyte count exceeds 4.0 × 109/L (see Chap. 1).

  • Normal lymphocyte count in childhood is higher than adults (mean ~6.0 × 109/L) until about 3 years of age (see Chap. 1).

  • Table 50–1 lists conditions associated with lymphocytosis.

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

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

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

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

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

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

  • Several key tests permit discrimination between polyclonal and monoclonal disorders. Flow cytometric immunophenotyping of cell surface markers (CD), serum protein electropheresis 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 Clonal Lymphocytosis

  • Neoplastic (monoclonal) proliferation of B cells, T cells, or natural killer (NK) cells.

  • Monoclonal B-cell lymphocytosis (see Chap. 56).

    — No associated clinical manifestations.

    — Some patients may develop CLL or another type of progressive lymphoproliferative disease (see Chap. 56).

  • Chronic natural killer (NK) cell lymphocytosis (see Chap. 58).

    — CD3−CD16+CD56+ lymphocytes

    — ...

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