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Leukocyte Alkaline Phosphatase Blood Test

Last updated June 4, 2016

What are other Names for this Test? (Equivalent Terms)

  • LAP Blood Test
  • Neutrophil Alkaline Phosphatase Blood Test

What is Leukocyte Alkaline Phosphatase Blood Test? (Background Information)

  • Leukocyte alkaline phosphatase (LAP) is an enzyme present in a type of white blood cell (leukocyte) called a neutrophil
  • Neutrophils are the most abundant type of white blood cells (WBCs), comprising 40-75% of WBC numbers. They are generalized WBCs responsible for a diverse array of immune activities, including inflammation and pathogen degradation
  • The Leukocyte Alkaline Phosphatase Blood Test helps determine the levels of LAP in a sample of blood containing neutrophils. The test is mainly used to differentiate between benign reactive increase in neutrophils and malignant conditions that show an increase in the number of neutrophils
  • Because there are advanced tests to diagnose blood cancers, currently the LAP Blood Test is only occasionally used in medical practice. The test is rarely used to help differentiate between white blood cell cancers, called lymphomas
  • The Leukocyte Alkaline Phosphatase Blood Test is scored by counting 100 neutrophils in a blood sample and assigning a grade based on the amount of dye they take up as part of the test, which indicates the abundance of leukocyte alkaline phosphatase

What are the Clinical Indications for performing the Leukocyte Alkaline Phosphatase Blood Test?

The clinical indicators for performing the Leukocyte Alkaline Phosphatase Blood Test include differentiating between severe neutophilia (leukemoid reaction) and myeloproliferative neoplasms from chronic myeloid leukemia.

Note: A benign reactive increase in neutrophils is called a leukemoid reaction.

How is the Specimen Collected for Leukocyte Alkaline Phosphatase Blood Test?

Following is the specimen collection process for Leukocyte Alkaline Phosphatase Blood Test:

Sample required: Blood 

Process of obtaining a blood sample in adults:

  • A band is wrapped around the arm, 3-4 inches above the collection site (superficial vein that lies within the elbow pit)
  • The site is cleaned with 70% alcohol in an outward spiral, away from the zone of needle insertion
  • The needle cap is removed and is held in line with the vein, pulling the skin tight
  • With a small and quick thrust, the vein is penetrated using the needle
  • The required amount of blood sample is collected by pulling the plunger of the syringe out slowly
  • The wrap band is removed, gauze is placed on the collection site, and the needle is removed
  • The blood is immediately transferred into the blood container, which has the appropriate preservative/clot activator/anti-coagulant
  • The syringe and the needle are disposed into the appropriate “sharp container” for safe and hygienic disposal

Preparation required: No special preparation is needed prior to the test.

What is the Significance of the Leukocyte Alkaline Phosphatase Blood Test Result?

The significance of the Leukocyte Alkaline Phosphatase Blood Test is explained.

  • A high value (greater than 95) for the test may point to a diagnosis of:
    • Neutrophilia (leukemoid reaction)
    • Myeloproliferative neoplasms
  • A low value (less than 11) for the test may point to a diagnosis of chronic myeloid leukemia

The laboratory test results are NOT to be interpreted as results of a "stand-alone" test. The test results have to be interpreted after correlating with suitable clinical findings and additional supplemental tests/information. Your healthcare providers will explain the meaning of your tests results, based on the overall clinical scenario.

Additional and Relevant Useful Information:

  • More advanced medical tests have largely replaced the Leukocyte Alkaline Phosphatase Blood Test, making it a rarely ordered test

Certain medications that you may be currently taking may influence the outcome of the test. Hence, it is important to inform your healthcare provider, the complete list of medications (including any herbal supplements) you are currently taking. This will help the healthcare provider interpret your test results more accurately and avoid unnecessary chances of a misdiagnosis.

What are some Useful Resources for Additional Information?

Please visit our Laboratory Procedures Center for more physician-approved health information:


References and Information Sources used for the Article:

Kee, J. L. (2010). Laboratory and diagnostic tests with nursing implications (8th ed.). Upper Saddle River, NJ: Pearson.

Martini, F., Nath, J. L., & Bartholomew, E. F. (2012). Fundamentals of anatomy & physiology (9th ed.). San Francisco: Benjamin Cummings.

Williamson, M. A., Snyder, L. M., & Wallach, J. B. (2011). Wallach's interpretation of diagnostic tests (9th ed.). Philadelphia: Wolters Kluwer/Lippincott Williams & Wilkins.

Helpful Peer-Reviewed Medical Articles:

McComb, R. B., Bowers Jr, G. N., & Posen, S. (2013). Alkaline phosphatase. Springer Science & Business Media.

Udristioiu, A., Iliescu, R. G., Cojocaru, M., & Joanta, A. (2014). Alkaline phosphatase isoenzymes and leukocyte alkaline phosphatase score in patients with acute and chronic disease: a brief review. British Journal of Medicine and Medical Research, 4(1), 340.

Bain, B. J. (2014). Blood cells: a practical guide. John Wiley & Sons.

Pagana, K. D. (2013). Mosby's manual of diagnostic and laboratory tests. Elsevier Health Sciences.

Jin, H. J., Bae, Y. K., Kim, M., Kwon, S. J., Jeon, H. B., Choi, S. J., ... & Chang, J. W. (2013). Comparative analysis of human mesenchymal stem cells from bone marrow, adipose tissue, and umbilical cord blood as sources of cell therapy. International journal of molecular sciences, 14(9), 17986-18001.

Wan, Z., & Hill, E. G. (2013). Characterization of common blood test abnormalities potentially aiding diagnosis of mast cell activation syndrome: a preliminary analysis. Blood, 122(21), 5240-5240.

Yoshida, Y., Katsurada, T., Oguma, S., Nakabo, Y., Yoshinaga, N., Kawahara, M., & Kawabata, H. (2013). Absent or extremely low neutrophil alkaline phosphatase activity levels in patients with myelodysplastic syndromes. Internal Medicine, 52(4), 479-482.

Snyder, M. L., Wiley, C., Molinaro, R. J., Ritchie, J. C., & Fantz, C. R. (2013). Falsely increased HCG in patients with high leukocyte counts. Clinical chemistry, 59(7), 1127-1129.

Reviewed and Approved by a member of the DoveMed Editorial Board
First uploaded: June 4, 2016
Last updated: June 4, 2016