Mehlman High Yield Practice Exam

Understanding leukocyte alkaline phosphatase (LAP) helps separate reactive leukocytosis from a malignant myeloproliferative process. In a leukemoid reaction, neutrophils are elevated due to infection or stress, and LAP activity is high because the neutrophils are functionally active in a reactive state. By contrast, chronic myeloid leukemia involves clonal proliferation of myeloid cells with low LAP activity, reflecting a malignant process rather than a reactive one. So when you see marked leukocytosis with a low LAP score, the pattern points toward chronic myeloid leukemia rather than a leukemoid reaction. Additional clues for CML include basophilia, SAMPLEsplenomegaly, and commonly the Philadelphia chromosome (BCR-ABL) or related molecular findings. Acute leukemias would typically present with blasts and different laboratory features rather than a low LAP pattern.