section name header

Introduction ⬇

These agranulocytes, the largest cells of normal blood, are the body’s second line of defense against infection. Histiocytes, which are large macrophagic phagocytes, are classified as monocytes in a differential leukocyte count. Histiocytes and monocytes are capable of reversible transformation from one to the other.

These phagocytic cells of varying size and mobility remove injured and dead cells, microorganisms, and insoluble particles from the circulating blood. Monocytes escaping from the upper and lower respiratory tracts and the gastrointestinal and genitourinary organs perform a scavenger function, clearing the body of debris. These phagocytic cells produce the antiviral agent called interferon.

This test counts monocytes, which circulate in certain specific conditions such as tuberculosis, subacute bacterial endocarditis, and the recovery phase of acute infections.

Normal Findings ⬆ ⬇

Absolute count: 200–1000/mm3 or 0.2–1.0 × 109/L

Differential: 2%–10% of total WBC count

Procedure ⬆ ⬇

  1. Obtain a 5-mL whole blood sample in a lavender-topped tube (with EDTA) and label the specimen with the patient’s name, date and time of collection, and test(s) ordered.

  2. Observe standard precautions.

  3. Count as part of the differential.

Clinical Implications ⬆ ⬇

  1. In monocytosis: A monocyte increase of more than 1000 cells/mm3 or more than 2.0 × 109/L or more than 10%. The most common causes are bacterial infections, tuberculosis, subacute bacterial endocarditis, and syphilis.

  2. Other causes of monocytosis:

    1. Monocytic leukemia and myeloproliferative disorders

    2. Carcinoma of stomach, breast, or ovary

    3. Hodgkin disease and other lymphomas

    4. Recovery state of neutropenia (favorable sign)

    5. Lipid storage diseases (e.g., Gaucher disease)

    6. Some parasitic, mycotic, and rickettsial diseases

    7. Surgical trauma

    8. Chronic ulcerative colitis, enteritis, and sprue

    9. Collagen diseases and sarcoidosis

    10. Tetrachloroethane poisoning

  3. Phagocytic monocytes (macrophages) may be found in small numbers in the blood in many conditions:

    1. Severe infections (sepsis)

    2. Lupus erythematosus

    3. Hemolytic anemias

  4. Decreased monocyte count (less than 200 cells/mm3 or less than 0.2 × 109/L) is not usually identified with specific diseases:

    1. Prednisone treatment

    2. Hairy cell leukemia

    3. Overwhelming infection that also causes neutropenia

    4. Human immunodeficiency virus (HIV) infection

    5. Aplastic anemia (bone marrow injury)

Interventions ⬆ ⬇

Pretest Patient Care

  1. Explain test purpose and procedure.

  2. Refer to standard pretest care for CBC and differential count. Also, follow guidelines in Chapter 1 for safe, effective, informed pretest care.

Posttest Patient Care

  1. Review test results; report and record findings. Modify the nursing care plan as needed. Counsel the patient regarding abnormal findings; explain the need for possible follow-up testing and treatment. Monitor for leukemia and infection.

  2. Refer to standard posttest care for hemogram, CBC, and differential count. Also, follow guidelines in Chapter 1 for safe, effective, informed posttest care.

Interfering Factors ⬆

see Appendix E for drugs that affect test outcomes.