LAP Score
- Sample Type
- Whole Blood (Smear)
- Fasting
- No
- Unit
- Score
Function
The Leukocyte Alkaline Phosphatase (LAP) score is a cytochemical test performed on a peripheral blood smear. It measures the amount of the enzyme alkaline phosphatase present within the granules of mature neutrophils. A technician stains the blood slide and scores 100 mature neutrophils on a scale of 0 to 4 based on the intensity of the stain, resulting in a final score between 0 and 400.
Why it is Ordered
The LAP score is primarily used to differentiate between two conditions that present with a very high white blood cell count:
- Chronic Myeloid Leukemia (CML): Where the malignant neutrophils are enzyme-deficient (Low LAP).
- Leukemoid Reaction: A normal, vigorous response to severe infection or stress where neutrophils are highly active (High LAP).
Associated Conditions
- Chronic Myeloid Leukemia (CML): Classically presents with an extremely low LAP score.
- Polycythemia Vera: Often shows an elevated LAP score.
- Leukemoid Reaction: Caused by pneumonia, sepsis, or severe inflammation.
- Pregnancy/Stress: Can physiologicaly increase the LAP score.
Why Context Matters
The LAP score is a subjective test because it relies on the technician's visual interpretation of staining intensity. Results can vary between laboratories. While historically important, it has largely been superseded by genetic testing for the Philadelphia chromosome (BCR-ABL1). If an LAP score is low, a second opinion should involve molecular testing to confirm or rule out CML definitively.
Lab ranges are statistical averages, not biological laws. "Normal" for a 20-year-old male isn't normal for a 60-year-old female.
Clinical References
Source-of-truth databases and clinical guidelines for LAP Score:
Official Sources
- Chronic myeloid leukemia: 2025 update on diagnosis, therapy, and monitoring - PubMedpubmed.ncbi.nlm.nih.gov
Research & Guidelines
- PubMed: LAP Score Clinical GuidelinesNCBI / PubMed
Related Indicators
Medically Reviewed by Dr. Binoy Babu, MBBS
Board Certified Doctor • 10+ Years Clinical Experience
Dr. Babu is a practicing physician dedicated to empowering patients with clear, actionable medical information. He founded 2opi to bridge the gap between complex lab reports and patient understanding, ensuring everyone has access to a reliable second opinion.
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