Leukocytosis :Significance of Monocytosis vs Lymphocytosis

Monocytosis (monocyte count greater than or equal to 10x109) may indicate :

    - an underlying malignancy, immunologic disease or chronic inflammatory process.
    - certain primary hematologic disorders such as drug-induced or other forms of neutropenia, hemolytic anaemias, or myelodysplastic syndromes.
    - the early phase of bone marrow recovery from myelosuppression or following intensive chemotherapy.


  • In adult patients lymphocytosis (absolute lymphocyte count greater than or equal to or > 7x109) is usually an indication of hematologic malignancy, in particular chronic lymphocytic leukemia.
  • CLL is described in the Lymphadenopathy program.

  • Lymphocytosis in adults also may occur in association with endocrine disorders, especially thyrotoxicosis or adrenal insufficiency.

  • In childhood and adolescence the chief causes are pertussis and acute infectious.

  • Atypical or reactive lymphocytes are characteristic of viral infections such as infectious mononeucleosis.

Lymphocytosis in Childhood

  • In childhood and adolescence, the chief causes of lymphocytosis are pertussis and acute infectious lymphocytosis.

  • Pertussis (whooping cough) may be associated with lymphocyte counts of 7x109 or more.

  • Acute infectious lymphocytosis is a mild, self limited disease usually asymptomatic, but occasionally characterised by fever, rash and upper respiratory symptoms. Lymphocytosis may reach impressive levels and persist for several weeks.

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