Which condition is characterized by a low LAP score compared to a high LAP score in leukemoid reactions?

Chronic myelocytic leukemia (CML) is characterized by a low leukocyte alkaline phosphatase (LAP) score, which is a significant distinguishing feature compared to conditions like leukemoid reactions that typically present with a high LAP score. In CML, the bone marrow produces an increased number of immature white blood cells, particularly myeloid cells, due to the underlying genetic mutation (often the Philadelphia chromosome). These immature cells usually express lower levels of alkaline phosphatase, leading to the decreased LAP score observed in CML.

On the other hand, leukemoid reactions, which are often triggered by infections or other stressors, typically result in an elevated LAP score. This high score indicates an active and effective response of mature neutrophils, which are seen in inflammatory conditions.

Understanding the differences in LAP scores helps in the differential diagnosis of myeloproliferative disorders, and specifically highlights how CML presents distinctively in laboratory findings when compared to reactive processes.