Leukocyte Alkaline Phosphatase

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Leukocyte Alkaline Phosphatase

Synonym/acronym: LAP, LAP score, LAP smear.

Common use

To monitor response to therapy in Hodgkin’s disease and diagnose other disorders of the hematological system such as aplastic anemia.


Whole blood (1 mL) collected in a lavender-top (EDTA) tube.

Normal findings

(Method: Microscopic evaluation of specially stained blood smears) 25 to 130 (score based on 0 to 4+ rating of 100 neutrophils).


Alkaline phosphatase is present in the cytoplasm of neutrophilic granulocytes from the metamyelocyte to the segmented stage of development. The study involves counting 100 neutrophils from a stained smear. Segmented and band forms are counted; eosinophils, basophils and other immature neutrophil forms are excluded. The reaction is subjectively scored from 0 to 4 based on the number of stained granules observed in the counted cells as well as the intensity of the staining. The number of cells counted is then multiplied by the score to arrive at the result. Leukocyte alkaline phosphatase (LAP) concentrations may be altered by the presence of infection, stress, chronic inflammatory diseases, Hodgkin’s disease, and hematological disorders. Low levels are associated with the presence of leukemic leukocytes while high levels are present in normal white blood cells (WBCs). The test has been used for many years as a supportive test in the differential diagnosis of leukemia.

As time from its inception has passed, and other technologies such as polymerase chain reaction (PCR) and FISH (fluoresence in-situ hybridization) have emerged, the LAP assay is used less often. The current World Health Organization classification of chronic myeloproliferative neoplasms does not use the LAP score; rather a consensus of experts have developed international criteria such as morphology, immunophenotype, genetics, and clinical features. PCR and FISH technologies are used to evaluate blood or bone marrow specimens collected in a sodium heparin collection tube. The testing can be used to identify BCR/ABL-1 or JAK2 gene rearrangements that assist in the classification and treatment of hematologic conditions such as CML, polcythemia vera, and other myeloproliferative neoplasms.

This procedure is contraindicated for



  • Differentiate chronic myelocytic leukemia from other disorders that increase the WBC count
  • Monitor response of Hodgkin’s disease to therapy

Potential diagnosis

Increased in

  • Conditions that result in an increase in leukocytes in all stages of maturity will reflect a corresponding increase in LAP.

  • Aplastic leukemia
  • Chronic inflammation
  • Down’s syndrome
  • Hairy cell leukemia
  • Hodgkin’s disease
  • Leukemia (acute and chronic lymphoblastic)
  • Myelofibrosis with myeloid metaplasia
  • Multiple myeloma
  • Polycythemia vera (increase in all blood cell lines, including leukocytes)
  • Pregnancy
  • Stress
  • Thrombocytopenia

Decreased in

    Chronic myelogenous leukemia Hereditary hypophosphatemia (insufficient phosphorus levels) Idiopathic thrombocytopenia purpura Nephrotic syndrome (excessive loss of phosphorus) Paroxysmal nocturnal hemoglobinuria (possibly related to the absence of LAP and other proteins anchored to the red blood cell wall, resulting in complement-mediated hemolysis) Sickle cell anemia Sideroblastic anemia

Critical findings


Interfering factors

  • Drugs that may increase the LAP score include steroids.

Nursing Implications and Procedure


  • Positively identify the patient using at least two unique identifiers before providing care, treatment, or services.
  • Patient Teaching:  Inform the patient this test can assist in evaluating for blood disorders.
  • Obtain a history of the patient’s complaints, including a list of known allergens, especially allergies or sensitivities to latex.
  • Obtain a history of the patient’s hematopoietic and immune systems, symptoms, and results of previously performed laboratory tests and diagnostic and surgical procedures.
  • Obtain a list of the patient’s current medications, including herbs, nutritional supplements, and nutraceuticals (see Effects of Natural Products on Laboratory Values).
  • Review the procedure with the patient. Inform the patient that specimen collection takes approximately 5 to 10 min. Address concerns about pain and explain that there may be some discomfort during the venipuncture.
  • Sensitivity to social and cultural issues,  as well as concern for modesty, is important in providing psychological support before, during, and after the procedure.
  • Note that there are no food, fluid, or medication restrictions unless by medical direction.


  • Potential complications: N/A
  • Avoid the use of equipment containing latex if the patient has a history of allergic reaction to latex.
  • Instruct the patient to cooperate fully and to follow directions. Direct the patient to breathe normally and to avoid unnecessary movement.
  • Observe standard precautions, and follow the general guidelines in Patient Preparation and Specimen Collection. Positively identify the patient, and label the appropriate specimen container with the corresponding patient demographics, initials of the person collecting the specimen, date, and time of collection. Perform a venipuncture.
  • Remove the needle and apply direct pressure with dry gauze to stop bleeding. Observe/assess venipuncture site for bleeding or hematoma formation and secure gauze with adhesive bandage.
  • Promptly transport the specimen to the laboratory for processing and analysis.


  • Inform the patient that a report of the results will be made available to the requesting health-care provider (HCP), who will discuss the results with the patient.
  • Instruct the patient to avoid exposure to infection if WBC count is decreased.
  • Recognize anxiety related to test results, and be supportive of perceived loss of independence and fear of shortened life expectancy. Discuss the implications of abnormal test results on the patient’s lifestyle. Provide teaching and information regarding the clinical implications of the test results, as appropriate. Educate the patient regarding access to counseling services.
  • Reinforce information given by the patient’s HCP regarding further testing, treatment, or referral to another HCP. Answer any questions or address any concerns voiced by the patient or family.
  • Depending on the results of this procedure, additional testing may be performed to evaluate or monitor progression of the disease process and determine the need for a change in therapy. Evaluate test results in relation to the patient’s symptoms and other tests performed.

Related Monographs

  • Related tests include biopsy bone marrow, calcium, CBC, CBC platelet count, CBC WBC count and differential, CT thoracic, gallium scan, Ham’s test, Hgb electrophoresis, hemosiderin, IFE, immunoglobulins, iron, laparoscopy abdominal, liver and spleen scan, lymphangiogram, mediastinoscopy, phosphorus, and sickle cell screen.
  • Refer to the Hematopoietic and Immune systems tables at the end of the book for related tests by body system.
Handbook of Laboratory and Diagnostic Tests, © 2013 Farlex and Partners
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