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INTRODUCTION

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  • Monocytes in the blood are in transit. They function in the tissues, where they mature into macrophages and participate in:

    • — Inflammation, including granulomatous reactions, atheroma formation, and tissue repair.

    • — Immunologic reactions, including delayed hypersensitivity.

    • — Reactions to neoplasia and allografts.

  • The need for macrophages in tissues also can be met by local proliferation of macrophages, not requiring increased transit of blood monocytes.

  • Ninety percent of blood monocytes intensely express CD14 (lipopolysaccharide receptor) but not CD16 and 10 percent have weak expression of CD14 and strongly express CD16.

  • Older persons have a striking decrease in the proportion of CD14+CD16– to CD14+CD16+ monocytes compared with younger persons.

  • Disorders rarely produce abnormalities of monocytes alone in the absence of other blood cell abnormalities.

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NORMAL BLOOD MONOCYTE CONCENTRATION

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  • The monocyte count averages 1.0 × 109/L in neonatal life, gradually decreasing to a mean of 0.4 × 109/L in adult life.

  • Monocytosis (in adults): >0.8 × 109/L.

  • Monocytopenia: <0.2 × 109/L.

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HEMATOLOGIC DISORDERS ASSOCIATED WITH MONOCYTOSIS

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Table Graphic Jump Location
TABLE 36–1DISORDERS ASSOCIATED WITH MONOCYTOSIS
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Neoplastic or Clonal Monocytic Proliferations

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  • Oligoblastic myelogenous leukemia (refractory leukemia with excess blasts or myelodysplastic syndrome).

  • Acute myelogenous leukemia (myelomonocytic or monocytic types).

  • Chronic myelomonocytic leukemia.

  • Juvenile myelomonocytic leukemia

  • Unusual type of BCR-ABL (p190)-positive chronic myelogenous leukemia with monocytosis.

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Reactive (Nonclonal) Monocytic Proliferations

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  • Neutropenic states: cyclic neutropenia; chronic granulocytopenia of childhood; familial benign neutropenia; infantile genetic agranulocytosis; chronic hypoplastic neutropenia.

  • Drug-induced agranulocytosis (transient monocytosis, especially in the recovery phase).

  • Chlorpromazine toxicity, monocytosis precedes the agranulocytosis.

  • Lymphoma.

  • Hodgkin lymphoma.

  • Postsplenectomy state.

  • Myeloma.

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INFLAMMATORY AND IMMUNE DISORDERS ASSOCIATED WITH MONOCYTOSIS

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Collagen Vascular Diseases

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  • Rheumatoid arthritis.

  • Systemic lupus erythematosus.

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