An enzyme found in mature leukocytes. Staining of LAP on peripheral blood smear is used to calculate the LAP score. A high LAP score is associated with an increased number of mature white blood cells (e.g., from leukemoid reaction or myeloproliferative disorders); a low LAP score is associated with an increased number of immature white blood cells (e.g., from CML).

Differ from Alkaline phosphatase.