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Subject: Leukocyte Alkaline Phosphatase (LAP)
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LAP, or neutrophil alkaline phosphatase, refers to a staining reaction of peripheral blood smears. It reflects the presence of LAP in neutrophils and their precursors. Normally, about 20% of mature neutrophils show stainable leukocyte LAP activity.
Normal range: score of 11–95. The scoring is based on counting 100 neutrophils and grading the stained granules from 0 to 4 on the basis of the intensity and appearance of the precipitated dye in the cytoplasm.
LAP stain helps differentiate a severe neutrophilia (leukemoid reaction) and myeloproliferative neoplasms, where it is increased, from chronic myeloid leukemia, in which case it is decreased or absent.
With the advent of modern diagnostic technologies, the use of LAP stains has diminished.
Polycythemia vera and essential thrombocythemia (occasionally it may be normal)
Trisomy 21 and Klinefelter syndrome
Chronic myeloid leukemia
PNH and pernicious anemia
Blood that is not processed soon after drawing may cause low LAP scores.
There is observer-dependent variability.