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Introduction ⬇

Neutrophils are the only leukocytes to contain various amounts of alkaline phosphatase.

The leukocyte alkaline phosphatase (LAP) stain is used as an aid to distinguish chronic granulocytic leukemia from a leukemoid reaction. A leukemoid reaction is a high WBC count that may look like leukemia but is not. In remission of CML, the LAP may return to normal. In the blast phase of CML, the LAP may be elevated.

Normal Findings ⬆ ⬇

40–100 LAP units

Procedure ⬆ ⬇

  1. Obtain specimen by capillary puncture, venous whole blood (EDTA), green-topped tube. Label the specimen with the patient’s name, date and time of collection, and test(s) ordered.

  2. Prepare smear and air-dry; stain with LAP.

  3. Make a count of 100 granulocytes and score (from 0 to 4+) as to the degree of LAP units.

Clinical Implications ⬆ ⬇

  1. Decreased values (0–15 LAP units)

    1. CML

    2. Paroxysmal nocturnal hemoglobinuria (PNH)

    3. Idiopathic thrombocytopenic purpura

    4. Hereditary hypophosphatasia

    5. Progressive muscular dystrophy

    6. Marked eosinophilia

    7. Nephrotic syndrome

    8. Siderocytic anemia

  2. Increased values

    1. Leukemoid reactions, all kinds of neutrophilia with elevated WBC count

    2. Polycythemia vera

    3. Thrombocytopenia (essential)

    4. Down syndrome (trisomy 21)

    5. Multiple myeloma

    6. Hodgkin disease

    7. Hairy cell leukemia

    8. Aplastic leukemia, acute and chronic lymphatic leukemia, chronic granulocytic leukemia

    9. Myelofibrosis, myeloid metaplasia

  3. Normal levels of LAP

    1. Secondary polycythemia

    2. Hemolytic anemia

    3. Infectious mononucleosis

    4. Iron-deficiency anemia

    5. Viral hepatitis

  4. Serial LAP tests can be a useful adjunct in evaluating the activity of Hodgkin disease and the response to therapy.

Interventions ⬆ ⬇

Pretest Patient Care

  1. Explain test purposes and procedures.

  2. 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.

  2. Counsel the patient regarding abnormal findings; explain the need for possible follow-up testing and treatment. Monitor for blood diseases.

  3. Follow guidelines in Chapter 1 for safe, effective, informed posttest care.

Interfering Factors ⬆

  1. Any physiologic stress, such as third-trimester pregnancy, labor, or severe exercise, causes an increased LAP score.

  2. Steroid therapy increases LAP score.

  3. CML with infection increases LAP score.